Portugal and the Dutch are somewhat different situations. Let's start with Portugal.

Portugal built most of its overseas empire, outside Brazil, very early on -- from the 1440s to about 1560 or so. At this point, Europe had a clear technological edge over most of Sub-Saharan Africa, but did not have such an edge over most of Asia -- except in a couple of key areas; see below.

Also, at this point, Asia was really far away. A trip from Portugal to India was a year each way, full stop. A trip to Malacca or Macao? Add another year, because if you missed the window for the annual monsoon, you might as well not bother. So Portuguese expeditions were really on their own.

Portugal had three strengths: aggression, technological surprise, and limited goals.

Aggression: it's hard to overstate just how aggressive the Portuguese were, especially during the critical period from 1495 to 1560. We normally associate aggression with famous warrior cultures like the Mongols or Zulus or some such. But the early modern Iberians were incredibly aggressive, and the Portuguese were arguably the worst. Small forces would regularly attack much larger ones, little expeditions would storm fortified cities, fleets would sail thousands of miles to launch an attack... and if they failed, they wouldn't necessarily back off; unless utterly crushed, they would regroup, come back, and try again.

This aggression was a force multiplier! Not only did it help the Portuguese win individual battles, but their reputation spread out before them. People got reluctant to cross them or to fight them, because they were, you know, fscking nuts.

(Ultimately, this aggression would cost the Portuguese dearly. In 1578, their King Sebastian led an expedition against Morocco. He was offered a very favorable peace, but instead chose to give battle against a greatly superior force. RIP King Sebastian and his entire army, and Portugal got absorbed into Spain for the next 70 years.)

Technological surprise: Asians had good steel, gunpowder, and well organized armies with effective early modern logistics. The one edge the Portuguese had: long-distance fully-rigged sailing ships armed with cannon. By the early 1500s these ships could usually outrun anything they couldn't outfight, and vice versa. Asians had large ships -- but they weren't armed with cannon, or if they were they were smaller and/or shorter-range guns. The Portuguese could stand off and batter them. This advantage let relatively small Portuguese expeditions regularly defeat larger naval forces, and gain effective control over the Indian Ocean.

(Exception: the Chinese under the middle Ming had cannon-armed ships that were a match, or nearly, for anything the Portuguese had. This is one reason that the Portuguese in East Asia were a lot less aggressive than they were in the Indian Ocean.)

Limited Goals: Finally, the Portuguese -- unlike the Spanish -- had limited goals. They didn't want to conquer continents or even kingdoms. For the most part, they wanted to get rich through trade. So their conquests were mostly limited to coastal trading ports -- Goa, Malacca, Hormuz, Surat, Macao. Even when they conquered larger areas, like along the Swahili Coast (later Mozambique) or Ceylon, it was usually opportunistic and restricted to a narrow coastal strip.

There's no Portuguese equivalent to Cortes or Pizarro subduing vast empires almost single handed. The Portuguese admiral Albuquerque was even more crazy aggressive than Cortes or Pizarro, but he wasn't out to conquer large areas of land. Albuquerque captured individual cities, not kingdoms or empires. More generally, the Portuguese tried to avoid fighting massive large-scale land battles, especially against powerful and organized opponents like the Persians, the Moguls or the Ming. Control the seas, exact tolls, capture a couple of strategic ports, and control trade -- that was their recipe for success.

Big Asian empires like the Persians or the Moguls or (especially) the Ming could have crushed the Portuguese if they'd really wanted to. The Moguls had the money and the technological capacity to build a fleet that could have wiped the Portuguese off the map. But... meh. That would have been a huge effort. And the Portuguese weren't an existential threat. Pirates and raiders who had captured some port cities, yes. Arrogant infidels with disgusting personal habits, sure. But from a grand strategic POV, they were a pain in the ass rather than a serious menace. The Asian land empires would occasionally take a swipe at Goa or Hormuz or whatever, and sometimes they'd succeed -- Bahrain was Portuguese for 100 years, but then the Safavid Persians took it back. But the Portuguese weren't worth a massive strategic reorientation from land to sea. A nuisance, sometimes a serious pest, but not worth building a massive navy and waging all-out war.

(Exception: the Ottomans actually tried this for a while, and almost succeeded. Unfortunately, without a Suez Canal, the Ottomans had trouble projecting naval force into the Indian Ocean. They gave the Portuguese a nasty scare, and seriously challenged their naval supremacy for a while, but in the end they couldn't quite pull it off.)

Phew. Okay, the Dutch now... anyone want to do the Dutch?

Okay, so the Dutch.

The Dutch colonial empire in Asia got started by cannibalizing the Portuguese colonial empire in Asia -- full stop. Eventually the Dutch developed trading posts and conquests of their own, but for the first 60 years of their Asian imperialism (c.1600 - 1650), they were snatching ports, bases and coastal colonies away from the Portuguese. They were successful in grabbing only a few -- Malacca, Ceylon, the bases on the Coromandel Coast -- but at one time or another they attacked pretty much every Portuguese possession in Asia. They besieged Goa intermittently for literally decades!

Okay, so -- why? Why did the Dutch attack the Portuguese instead of trying to set up their own parallel raiding / trading empire?

Well, you may remember that after the Portuguese King Sebastian got himself killed in 1578, Portugal got absorbed into the Spanish empire. And the Dutch were at war with Spain. So they were also at war with Portugal. If they wanted to break into the Indian Ocean, the Portuguese were going to fight them anyway. So... might as well kill two birds with one stone: weaken Spain while grabbing those highly lucrative Portuguese colonies.

Now here it gets a little ironic: the Dutch in the early 1600s were in a very similar position to the Portuguese in the early 1500s. They had a slightly better ship / weapon package -- not overwhelming, but in an even fight they had an edge. And they were extremely aggressive, driven by a combination of capitalism and muscular Protestantism. (They had a famous slogan: "Despair not, spare your enemies not, for God is with us." But -- like the Portuguese before them -- they started off kind of derpy. They didn't know much about the Indian Ocean, and at first tended to blunder in their diplomacy.

Meanwhile the Portuguese were the incumbents. They weren't used to facing a rival European naval power, with ships and seamen that were every bit as good or better. That was a nasty surprise. But OTOH after 100 years in Asia, they had well-developed, well-fortified colonies. They also had a modest population base to draw on, because there were Portuguese settlers, half-castes, and converts.

So it was actually a fairly even match. The Dutch ended up with some successes; they ripped away several of Portugal's bases and colonies, and they ended Portugal's golden age for good. But they couldn't take Goa, and in the end the Portuguese Asian empire survived, albeit smaller and weaker.

Now, the Dutch did have one very important colony that they /didn't/ steal from the Portuguese: Batavia, today known as Jakarta, the capital of Indonesia. The Dutch made a very deliberate decision to build up their footprint in what's now Indonesia, because there was a relative strategic vacuum there. Once you got east of the Sultanate of Aceh, there were no large, organized states -- it was dozens of little kingdoms. They weren't necessarily pushovers; some were wealthy and some were warlike. But none had the kinds of resources that big Asian states like the Mughals or the Tokugawa Japanese could throw around, never mind the Ming. The Portuguese had gone to the Moluccas, and did some trading for spices, but they weren't there in force. So it was a more promising theater. The Dutch went there in force, and developed Batavia as a counterweight to Goa.

Here's a thing, though -- for the next 100+ years, Batavia was a small coastal colony. The Dutch gradually gained control of a strip of land along the north coast of Java, and slowly sprinkled more forts and trading posts around the archipelago. But when you look at a map of Indonesia today? The Dutch showed up in the early 1600s, but 90% of that map was still independent until the late 1700s, and large chunks of it were still independent well into the 1800s.

It's easy to look at a colonial map and think "wow, tiny little Holland grabbed this huge chunk of Asia". Well yes eventually they did. But most of that conquering came later, when Europe's technological and organizational lead over SE Asia had grown quite large. In the 1600s and early 1700s, the Dutch empire in Asia was a constellation of ports and forts and a few coastal strips, much like the Portuguese empire had always been.

So to bring it back to the OP's question -- the Portuguese and Dutch did carve out impressive and profitable empires in Asia. But they weren't mass conquests, or at least not at first. It makes more sense when you realize that these were maritime empires of ports and forts based on trading, raiding, and extorting tolls, not land empires based on large-scale conquest.