Here's a riddle for you

So a man lives on the tenth floor of an apartment building. Every morning he wakes up, gets ready, and leaves his apartment to go to work. He takes the elevator down to the lobby and takes a cab to work. Every day he comes home to his building and gets in the elevator and rides it up to only the sixth floor, from there he takes the stairs up to his apartment on the tenth floor. He does this same routine everyday... except on rainy days; on rainy days, when he comes of from work, he takes the elevator all the way to the tenth floor. Why? Why doesn't he take the elevator to the tenth floor everyday instead of just rainy days?

I leave you to ponder this