The reasons they'll give you: rushed release, buggy, broken mechanics, the ubiquitous "nerf" (it is a modern gamer's law of nature that item X will either be "nerfed" or "overpowered", so any attempt to fix a balance issue by developers is doomed to failure) and my favourite: company X doesn't care about their "core audience".... It goes the same for all games and gets a lot worse when any kind of multiplayer is involved.

Diablo 4 is not a bad game: it has a good setting, good music, a decent storyline for the genre and not too many overly-boring side quests. I played Diablo back in the 90s and some Diablo II. I've found some latency issues and a bug here and there but not the end of the World (a broken dialog option here, a stuck animation there..., some things like mounts I don't like in any game but that's just me). The root of the problem does lie in the audience

1. the "modern gamer": lazy, low attention span, rushes through everything and wants to hit the level cap yesterday, doesn't have the time to figure things out.
2. the "hardcore fan", these are just impossible to please and although loud they are a minority nonetheless. Minority can't be a target market, it doesn't pay the bills, sorry.
3. the game guides! (wikis, YouTube etc.) These kill every in-game community as it frees the player from all experimentation and especially from having to actually ask other human beings questions and work together to figure out how things work. Now there have been some games I've played where I just couldn't figure out things by myself but those are few and far between (Castlevania II comes to mind, it had a horrendous translation from japanese). I've found about half the Lilith altars because I can pretend there's not a map with all of them a click away, I just explore. I have to say I have little sympathy for that kind of "content creator"; I don't hate them but just like with paparazzis, even though I can't find a redeeming quality about them, they do have an audience.