When I watch some bad movies, I cannot figure out why they were made. The recent “Dirty Grandpa” seems to exist so that Robert De Niro can say the “N-word” on-screen and stick his flaccid penis in Zac Efron’s face. Its director, Dan Mazer, is an Oscar nominee. Was this the kind of movie he dreamed of making when he got into film? But in the case of “Zoolander 2,” it’s hard to fathom why anyone wanted to make this particular version of it.