Many reasons.
But one of the interesting ones is that most attacks in the game have some form of being blocked. Those that aren’t have been:
Sym 2.0’s secondary: Removed from game, was extremely slow.
Dragonblade: Is an ultimate. On a 200hp hero.
Reinhardt’s Charge: Huge telegraph, easily punished, can’t be cancelled, removes 2000hp shield
Moira Orb: Slow, can only do 200hp damage
Hero Melee: Shortest of ranges, 30hp max
Doomfist: Fast, has 2 unblockable attacks, only one needs to be up close with other abilities to facilitate, both CC, one can 1hKO, has to be in the enemy team (but abilities create extra temp health)
Aye it’s good to have a hero who can play regardless of shields, but when it comes at the cost of being counterable by only zarya bubbles (an ability only 1/31 heroes has that has cooldowns higher than said abilities) It distinctly feels unfair to play against. Especially when these abilities have no severe downside.