Most champs like Yasuo, usually have 1 clear clear counter. But Yasuo's windwall allows him to essentially neglect that counter. Riot has already went on a crucade to make every cc into a projectile skillshot, hence, considering that he's already got a 0 cooldown dash, so if you manage to hit him, you should be rewarded with maybe a kill or at least making him unable to fight you (in a teamfight). The windwall however adds an extra layer where is immune to skillshot/projectiles, making him "immune" to CC, and he can dash/walk around his wall avoid almost all forms of damage except melee (which is where HE WANTS to fight his opponents). And even if you manage to hit him, most experienced yasuo players will at least somehow have reacted an managed to put a windwal between your team and him, so he's safe to wait out the duration of the CC (also most movement cc is roots etc so in some of them he can still cast his windwall). So your damage will be lost (due to his shield) and the CC due to his windwall, so when you get closer to take advantage of your cc on him, he turns the fight.