Ahem.
Allow me to break this down.
First off: See this guy? You may not recognize his name, but he actually voices a character from the Loud House named Chandler.Now for those who've seen the Loud House and know who Chandler is and his personality? Yeah....
That's number 1.
Number 2: This guy simply isn't Zack and that's who everyone wanted. It's just that simple. And while Daniel is doing his best, he simply isn't up to snuff in comparison.
Number 3: Most people expected Teen/Future Steven because that's the version you'd expect for a fighter game, but the devs went for the more "marketable" version of Steven. So...yeah. That made no sense. I don't normally diss what PFG does but the most marketable version would be the one the majority wants, which is Teen/Future Steven.
Number 4:Media Illiterate idiots hate Steven in general. Notice how there are fanarts of Steven being JoJo Stomped by Shaggy, Batman, Finn and even GARNET all just to spite him. It didn't help that this is Kid Steven they are using in the game(the most naive and immature version of Steven).
I think that pretty much covers it.