Does riot not see any issues with him?
Half of the players don't like playing against him and akali's been nerfed to death people are starting to remember to ban yasuo. He's not worth the heartache of learning how do deal with him when you can easily remove him from the game. Now because half of the player base hates him enough to ban him out, his mains can't play him half of the time. If he does get through it's probably because the other team's top laner is planning on playing him or is still scared of akali.
I get that he's a polarizing champ. That's fine. A 51% ban rate however means something is wrong with the champ. There's a difference between champs you hate but can deal with and champs who you feel are worth your vote to delete from any one match.
However, is there nothing riot can do to keep him fun to play for his mains while lowering how toxic other people feel like he is to play against?