Adapted from a previous answer of mine.

Short answer:

Equipment was a factor. Iraqi T-72M1s lagged behind the Soviets' latest T-72Bs and T-80Bs. Iraqi tanks had thinner armor, worse optics, and less-effective ammunition than Soviet tanks. Many Iraqi units didn't even have T-72s, and had to use obsolescent T-62s and T-55s.

The Iraqi Republican Guard's Tawakalanah Division and the Iraqi Army's 12th Armored Division were defeated at 73 Easting for many reasons. Part of it was poor tactical deployment too close to a reverse slope that let the Americans get too close. Part of it was bad assumptions about where the Americans would come from. Part of it was technical inferiority.

But the biggest reason the Iraqis lost at 73 Easting was because Americans in 2nd Armored Cavalry Regiment were incredibly well-trained and well-prepared. They made excellent use of speed, surprise, and violence of action to take apart the Iraqis before they could react.

Long answer:

Much Iraqi equipment was obsolete by Soviet and Western standards. The Iraqis were still operating large numbers of outdated T-55s and T-62s in 1991.

Iraqi equipment was sometimes comparable to some Soviet weapons. The cream of the Iraqi armed forces, the Republican Guard's armored divisions had T-72M1 tanks and BMP-1 armored personnel carriers they'd imported from the Soviet Union. However, Soviet exports outside the Warsaw Pact tended to be less-advanced (you'll sometimes see Soviet exports derided as "monkey models"). Quite sensibly, the Soviets didn't want to export their latest technology and have it fall into Western hands. Armor historian Steve Zaloga writes:

As a result of the USSR’s export policy, clients such as Iraq did not receive tanks comparable in quality to the best Soviet tanks. In 1990 the best Iraqi version of the T-72 was the T-72M1 – roughly equivalent to the Soviet T-72A, which was already a decade old and not as well armored as the newer T-72B or the preferred T-80B series. Just as importantly, the Soviet Union did not export its best tank ammunition: the Iraqi army relied primarily on second-rate ammunition for its T-72 tank.

This brings us to another issue. The Iraqis' ammunition was a generation behind the Soviets' in 1991. Zaloga again:

…the best Soviet APFSDS around 1990 was the 3VBM-13 Vant, which had a 3BM-32 depleted-uranium penetrator with penetration capability of 560mm at 2km – about double the performance of the 3VBM-3 used by the Iraqis.

Many Iraqi tanks were also old and tired by 1991, as Zaloga notes:

Barrel life was a significant issue for Iraqi tanks as a large proportion of the inventory had been employed during the Iran–Iraq War and the Iraqi army was not especially diligent about keeping its equipment in prime condition; accuracy suffered due to tube erosion.

But here's the thing, very little of this mattered at 73 Easting. Only one American vehicle was hit at 73 Easting: an M3 Bradley from Ghost Troop - it wasn't even hit by a tank, but by 73mm round from a BMP-1 APC (which had already been hit by an sabot round from an M1A1 that didn't disable it). Most Iraqi tanks were destroyed before they ever got a shot off. The ones that did get fire back tended to miss short.

This is where we get to the important part: armored warfare is NOT a Top Trumps "Who Has the Best Tank" contest. What happened at 73 Easting had more to do with human factors than it did equipment.

The Iraqis did a great deal right before 73 Easting. Then-Captain H.R. McMaster, commander of 2nd ACR's Eagle Troop later wrote:

The enemy commander, Major Mohammed, and his soldiers knew the ground well. The unit had used the village for billets as they conducted live fire training. Mohammed, who graduated from the Infantry Officer Advanced Course at Fort Benning, Georgia thought it was the ideal ground from which to defend. Unaware of our brand-new global positioning system capabilities, he assumed that we would have to move along roads to avoid becoming lost in the featureless desert. He organized his defense along the road by fortifying the village with anti-aircraft guns to be used in the ground mode, machine guns, and infantry. Mohammed’s defense was fundamentally sound. He took advantage of an imperceptible rise in the terrain that ran perpendicular to the road and directly through the village to organize a reverse slope defense on the east side of that ridge. He anticipated that upon encountering his strong point at the village, we would bypass it either to the north or south. He built two engagement areas or kill sacks on the eastern side of the ridge to the north and the south of the village, emplaced minefields to disrupt forward movement, and dug in approximately forty tanks and sixteen BMPs about one thousand meters from the ridge. His plan was to engage and destroy us piecemeal as we moved over the crest. Hundreds of infantry occupied bunkers and trenches between his armored vehicles. He positioned a reserve of eighteen T-72s and his command post along another subtle ridgeline approximately three thousand meters further east.

Unfortunately, the Iraqi assumption about the Americans using the road was wrong, since the Americans had GPS and could navigate cross-country. The minefields were ineffective at stopping the Americans and did little serious damage, even though the American vehicles hit several mines (the exploding mines took the path of least resistance and blew into the soft sand, instead of the hard steel tracks). The Iraqis' reverse slope defense was too close to the ridge, so they didn't have much time to react when the Americans crested the ridge.

73 Easting is more an American victory than an Iraqi defeat and was a soldier's victory. 2nd Armored Cavalry Regiment (2nd ACR) was an extraordinarily well-prepared unit. They'd drilled intensively in Germany. They'd drilled intensively in the Gulf. They were highly-motivated, well-lead, and extremely self-confident. Yes, 2nd ACR had the cutting-edge Bradley and Abrams. But they were successful at 73 Easting because they were prepared to make the most of their equipment and not simply because they had great tanks.

When 2nd ACR made contact with the Tawakalnah Division, they reacted faster than the Iraqis could respond. Speed, surprise, and violence of action are critical ingredients of modern warfare and the 2nd ACR made the most of all three.

https://m.youtube.com/watch?v=jsS9oLAoW8g - A conversation with 2nd ACR's 73 Easting veterans. Note the discussion about 2nd ACR's intense training and preparation. Well worth a watch.

Before I end, I wanna plug Ken Pollack's excellent book Arabs at War. We often get the American perspective on the Gulf War, but Pollack does an excellent job showing the Iraqi side of things. He makes a good point about the limited Iraqi successes you don't always hear about:

The Tawakalnah fought measurably better than its counterparts in the regular army, although it still performed far below Western standards. In particular, its men destroyed and damaged more U.S. M-2 and M-3 infantry try fighting vehicles than any other Iraqi division and actually put out of action four U.S. tanks a feat no other Iraqi unit was able to accomplish.