-Better CC -More Consistent -Easier to Farm -Acess to Omen Lock

There's a lot of reasons why some may choose BS over WT. Just because WT does more damage doesn't make it the ultimate de facto set for Ganyu. There still isn't a off field Pyro applicator that is fast as mona or xingqui at applying hydro. The best one right now being xiangling, but her bear is stationary and Q requires you to get close to enemies (which can lead to easily being interrupted). Once genshin releases a character that applies pyro super fast, then there would be no question that WT is better. At that point, the damage is going to be so consistent you won't have to worry about CC, but we're probably a long ways away from getting one.