Because the champion is very forgiving and overloaded.
He's manaless, generates a free shield by moving, steroid passive that's probably one of the strongest in the game, mobile, an ability that blocks every projectile including ults, and his numbers are just a mess.
He's abused items and masteries to the point he got them nerf'd for everybody else, not to mention that despite being so game-breakingly overloaded Riot gives him a pass and leaves him untouched even when he's clearly disgustingly safe and strong.
Not only is he a disgusting champion but his players are by far some of the most toxic shitters in game.
Shit, just recently he had several bugs that made him deal more damage than intended and it took Riot ages to get around giving it a bandaid fix despite the community begging riot to fix that shit.
But you know what? all the reasons I stated aside; the reason I truly despise Yasuo is because Riot clearly favors him just like with other "play maker, lone wolf, insane damage carry" type champions.
He falls on the same category as Lee sin, Riven, Zed, Rengar.
Do you know what those champions all have in common? they're flashy, popular with the kids, and Riot makes money out of them by constantly pumping out skins for them and keeping them viable even in a meta that's supposed to make them weaker.
All those champions can shit the bed the entire game and still somehow stay relevant late game, yet for some reason they're never toned down or truly nerf'd because Riot knows that if they give these champions an actual weakness to play against then their playerbase would plummet which would just result in less sales for Riot.
Did that answer your question?