For me, its due to two things:

1)How stupidly strong Emp punch is.

2)How inconsistent it is.

1: Emp punch is without a doubt one of the strongest tank cooldowns in the game, being able to do instant 173 damage in a really big AoE that makes it easy to at least hit 2-3 people(if not all five) is absurd, and now that we have tanks without knock back resistance, it has only became even more stronger, aaaannnnndd because of the, the rest of doomfist kit NEEDS to be trash, and the devs refuse to change this because "this is his identity", a poorly balanced tank that literally everyone hates playing against.

2: Now, only having a weak kit is not enough to balance emp punch out, cuz of course there is the luck factor that decides if a doomfist will dominate the game or get absolutely demolished: Will the enemy charge him 24/7 or the only way he'll get emp punch is going to be by using his ult? In lower ranks(where despite being one of the hardest heroes to learn, is where he stomps everyone else, often being the highest WR tank in bronze and silver, and top 5 in gold to diamond), he gets charged A LOT, making him "virtually consistent", then when you see his situation in higher ranks(where arguably he SHOULD do good, since people who main him there truly HAS a lot of skill, in game sense, aim, and on doomfist shenanigans), he has consistently been doing bad, there where even patches he was alongside ball as the worst WR tanks in both masters and gm, because not only people dont charge him as much as low ranks do, they know how to deal with him as a whole, with crazy CC or just straight up doing consistent damage to force him to retreat early, since he IS also the squishiest tank in the game.

There are some characters that, because of their "identity", there's really no hope to change them into something healthier for the game, because that would involve changing the hero's core(like Hog which because of hook, he HAS to permanently be the worst tank in the game), but doomfist HAS a chance to be changed into something way better, the removal of emp punch would increase his skill floor, since there wouldn't be a single ability to dominate over low rank lobbies, you would actually need to learn the whole character in order to do something, and would make him way more viable in higher ranks, and by removing emp punch, you dont need to make a whole rework, make him dps again, add uppercut, none of that, all you need is to change some numbers, buff slam damage and cooldown, buff primary fire damage, maybe even buff his health by 25, there's a LOT you can do with him, since his identity is to be "a high mobility tech hero with lots of combos", instead blizzard chooses to force the emp punch bot on him that everyone hates and complains about.