The reason why Yasuo has such a huge playrate, and not a very big banrate

This will be a purely statistical study in DRAFT mode. Blind pick is not taken into account.

Yasuo on average has a playrate of 30% in draft mode. This means that he is in 30% of all games. However, this is not PICK rate. Only ONE team can have a Yasuo, so it's entirely possible that both teams have a Yasuo player and one got it before the other. With a 30% playrate, this is pretty likely. So I'm going to say Yasuo's pick rate is in reality about 45%.

Only 60% of players get a ban in draft mode. With this pick rate of 45%, this means that about half the time, Yasuo will be in YOUR game, regardless of which team they are on. 60% of the time that you get that coinflip of having a Yasuo in the game, that means that at least one of the ban slots will not be yasuo. And if the yasuo is on your team, this means that half of the bans are not going to be Yasuo.

This means AT MOST there will only be three slots for a Yasuo ban, and that Yasuo will be in your game half the time. You also have to discount the fact that you will not always get a ban.

TL;DR The reason Yasuo has such a high playrate and no banrate is because many many factors narrow it down to a very large portion of the time as little as 2 ban slots only have a chance at banning Yasuo