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Adding unique animations to attacks is as essential for adding personality to a pokemon as its design is. Pikachu is a pokemon you'll have with you for literally the entire game (you can't box it) and it has no choice but to learn Double Kick (it learns it before it has all 4 move slots filled). I don't care if Caterpie has a special animation for Electro Web, but giving commonly-used pokemon custom animations for their commonly-used/signature moves really should be standard at this point.
Currently, many people will use pokemon they like over pokemon which are strong. Why shouldn't this be a thing for attacks as well? Mega Kick on Kabutops might be a wasted moveslot, but if it looks cool and I like it, I might end up keeping it over some other move in-game. It adds more personality to mons and makes the battles more dynamic.
For most attacks, these animations are at most 2 seconds long, and you don't even need to do every attack for every mon - if you restrict it to fully-evolved mons, starters, and shillmons like Lucario, that pretty much cuts the dex in half. Status moves largely don't need custom effects, and things like beam attacks are mostly the same. It would take work to implement, but it's not the ridiculous ask that some people are pretending it is.