I don’t speak for everyone here but from what I know and remember:
•Too many Characters
It used to have a simple roster but with new additions, although they’re great, It’s hard to balance the characters
•Undeserving Nerfs/Buffs Changes
Some people don’t like the changes of the Heroes. Some made certain heroes worse and some overpowered.
Back then, Mercy can ressurect 5 teammates for her ultimate (now can only Rez 1 person w/ a 30 sec cooldown) and Symmetra can provide regenerative shields for teammates (now can only summon a giant barrier on the map/area)
Blizzard attempted to make players play Support roles, thus releases Priority Passes. It’s not very effective..
Let’s say you wanna play Damage role, the queue to enter a match will take long because almost everyone wants to play Damage
That’s all I know, but again I don’t speak for everyone. It’s still a fun game though, slightly chaotic