That's like asking why Lady Gaga dresses so weird. Every artist, in any type of music or creative works, has their own style in which they follow throughout the creation of their works. He likes wearing hats and using tuxes that's his thing. I guess he was just wearing it because he wanted to look fancy when he played the piano for the girl he was bringing it to, but that wasn't the idea of the video, it was to show all the pain he would go through for that girl.
Because he thinks it's super fly?