Why not make only 2 first bans simultaneous, and keep the rest as it's now?

because riots fear is that instead of a handful of outliar champs who get banned every game graves/yasuo ....

they will end up with 10 champs who are consistently banned above a really high about like 60%+.

basically you still only have 5 bans, instead of the promised 10, because you wont be able to see what the enemy team bans.

down from the effective 6 bans.

Because they're also increasing the speed of starting a game with this system. I think it's a good compromise.