So pirates are often portrayed as wearing normal seamans clothing and using sabers, pistols and muskets. But wouldn't it make sense to use spears/pikes for their superior reach and light armor like the ones the Conquistadors wore to atleast protect against light injuries?
There's a weapon literally called a "boarding pike". It was about a 6 to 8 foot polearm, often with a hook. It's purpose was what is on the label, to be used in boarding and repelling boarders. With the often damp conditions, frequent rain, and limited use of firearms, long firearms were used as a shock weapon and multiple single shot pistols would be carried at one time. That's why swords are so heavily associated with pirates and naval battles in the age of sail. By the time you go to reload in close quarters combat, you've been stabbed twenty times (which is why some pistols even came with a mini-bayonet) After that, if the victim was still resisting (actual pitched battles between pirates and their targets were rare), then it became a hand to hand fight.
Boarding pikes, with their hooks could be used to grab ropes, dig into the wooden rails and hulls of ships, and into people. Obviously. They're simple easy weapons. It's a sharp pointy stick.
As far as armor, they would be less common, in fact, I can't recall any accounts of pirates in armor (at least among Western Hemisphere pirates) What would be the point? They're heavy so if you fell overboard it wouldn't help your swimming situation (a surprising number of sailors in the period couldn't swim), most pirate attacks ended without combat (they usually went with shock and awe to make people surrender before a single shot was fired), and trying to scrabble over rails, ropes, barrels, livestock cages, and the other items found on a ships deck in a metal breast plate would restrict your movement. Besides, by the time of the Golden Age of Pirates (roughly 1700 to 1730) armor had largely fallen out of use. Perhaps some seadogs, freebooters, corsairs, or others from the 15th, 16th, or even 17th Century would have had one, but even then they would have been rare.
- Little, Benerson The Sea Rover's Practice: Pirate Tactics and Techniques, 1630~1730
Edit: To understand why armor and even advanced tactics was largely unnecessary for pirates, you have to understand that the big galleon vs. galleon/ship of the line fights you see in movies involving pirates were so rare, they're actually noteable moments in history.
Pirates, despite the romanticism of community and freedom, were thieves. If you're dead, you're not spending those coins on prostitutes and booze. Pirates preyed on merchants, not treasure galleons for the most part. Even when they did they picked off stragglers or snuck up in the night. Merchants weren't heavily armed and were not inclined to fight. Simply running up the flag and chasing them, maybe a deliberately missed shot or two, and they surrendered. More often than not, when a pirate ship came across a well armed naval vessel, they tucked tail and ran. Most fights between a pirate crew and a merchant crew ended pretty quickly. Common sailors of the age weren't exactly paid well, often disliked the captain, and had no inclination to fight. Pirates didn't even want to slaughter and rough up a crew. If you killed everyone, they'd be more likely to resist. Mercy was reserved for the common merchant crew (because guess who the recruiting pool was), death and torture for the merchant captain.
I want to answer the question from a different perspective: that of pirates in the east, with a focus on the Japanese pirates. For simplicity sake, let's call them kaizoku (海賊), because getting into the nuances of "pirates" versus "pirate-like navies" (suigun, 水軍, acting in less-than "navy-like" fashion) is a massive beast. Kaizoku wardrobe and weaponry would vary, but they absolutely used armor at times and weapons such as spear and naginata (薙刀, like halberds). I will also throw out the term wako (倭寇) for Japanese pirates, though that terms was not used in Japan at the times; it was used by Korea and China. Kaizoku is the native term.
Let's categorize these pirates into two groups (again, oversimplification): coastal raiders and inland marauders. Coastal raiders tended to be more lightly dressed at sea for manueverability and because the threat was not as great by the coastal powers in China at the outset. Famous General Qi Jiguang actually called the military methods and unarmed martial arts in China at the time as huafa (花法, flowery methods) in his book Lianbing Shiji (練尽層邃, Actual Record of Military Training). Coastal guards would flee and hide when wako ships appeared on the horizon. This is the same Qi Jiguang who wrote probably the most well known Chinese martial manual Jixiao Xinshu (紀效新書), fought Japanese wako, and supposedly snagged a copy of the Kage Mokuroku (陰目録) which got included in his famous work.
The Kage mokuroku is a reference to Kage Ryu (陰流, or Kage no Ryu 陰之流), one of the four "source" schools of "swordsmanship" in Japan, founded by Aisu Ikosai, who supposedly was a kaizoku at some point. Kage Ryu was inherited by Kammiizumi Ise no Kami who founded Shinkage Ryu, which was passed on to Yagyu Sekishusai (among others) who formulated Yagyu Shinkage Ryu, arguably the most famous martial art school in Japan. I bring this up because the Kage Ryu included methods of using swords, spears, etc along with special ashi sabaki (足捌, leg "movements"... it's complicated) that included teachings on how to walk, run, jump, slide, etc on ships. It was a strong art, strong enough that Qi Jiguang would include some of it's sword, spear, and leg movements in his martial art manual. And those concepts can be found in other martial art schools of the time, including those associated with piracy.
Kaizoku were found more inland, around the Japanese coast. Sometimes provincial navies would be part of these groups. Those pirates faced a bigger threat with shorter voyages, while also enjoying the benefit of friendlier ports, which all lead to different tactics. Often times pirates would wear do (胴, body armor) and kabuto (兜, helmet) while leaving their sleeves and leg guards off. Ship captains would wear the full ornate suit because that's what commanders did in the Sengoku and early Edo periods. Swords, spears, naginata, and bow/arrow were still used, but there were other unique weapons like kusari kagi (鎖鈎, hooking chains) that found usage. Kusari kagi would be hooks or balls of iron attached to the end of chains, used either in hand like swinging a rope, or attached to the end of a stick of varying lengths. Usage of said tools is found in styles of Japanese martial arts of the time as well, which is another point of contrast to western piracy (no pirates specialized in, say, "Blackbeard's Way of Fencing"... that I'm aware of, at least!). Spears would also see augmentation to things like kamayari (鎌槍, sickle spear) which would be a straight spear that had one or more blades/protrusion coming out the side that would be used to entangle and capture other weapons, clothing, etc.
I would also point out that even though sword is featured prominently in piracy, there was no "dedicated sword school" in existence in Japan at the time (through end of the Sengoku Jidai). Schools like Katori Shinto Ryu, Kage Ryu, Chujo Ryu, everything that made up the Kyo Hachi Ryu, and traditions that emerged during the Sengoku Jidai/early Edo periods were sogo bujutsu (総合武術), complete schools with teachings often based on spearmanship than sword. The way of using the sword was often times derived from the way of using the spear, given the spear's prominence in warfare. For example, Kamiizumi Ise no Kami, founder of Shinkage Ryu, was recognized as a master of spear more than a master of sword, even if Yagyu Shinkage Ryu is recognized as arguably the most famous sword school in Japan's history. One of Kamiizumi's students was the founder of Hozoin Ryu, a famous school of spear. Thus with kaizoku and pirates in general, teachings from those with skill would often be based on more universal principles and methods applied specifically to swordsmanship... in my opinion, at least, based on studying history and teachings of budo in Japan.
In short, pirates of the east (particularly Japan) were a good bit different than the typical western "pirate" image we think of. They were resourceful, organized, and made use of different armors/weapons when and where appropriate.
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