Like most of the buffs this patch, it's because they want him to be picked in worlds. It's not bigger because he's already doing well.
This is correct. Yone is balanced (neither OP nor UP) but he is on the lower side of that band, so we figured we could do a low-risk pro facing buff. We looked at Yasuo as well but he, while also balanced, is on the higher end of balanced so we figured it was not worth the risk.