In a huge study on the way people react to movie trailers, they discovered that one of the strongest indicators as to whether we'll see a movie is the actors in it. And how excited we are to see those actors is based on whether or not they're appearing in the same type of movie we've already seen them in. So while we might make fun of Johnny Depp for playing "wacky clown thing" in like 30 different movies, on paper it's a pretty solid career move. After all, look at the highest-grossing movies of 2014: we have Transformers: Age of Extinction (featuring Mark Wahlberg as a dumb man's man), Guardians of the Galaxy (featuring Chris Pratt as an idealistic goofball and Zoe Saldana as a sexy alien with weird skin color), and Dawn of the Planet of the Apes (featuring Andy Serkis as a CGI monster).
Naturally, this puts movies with unique premises or weird tones in really difficult situations -- common sense would indicate that key demographics are starving for something new, but if you look at the research you'll find that people don't even watch trailers for movies when they don't already like the genre. Which is why they fudge interesting movies into boring, cookie-cutter shapes: Don Jon was advertised as a romantic comedy even though it's more or less an anti-romantic comedy about cougar widows and porn addiction. Drive was sort of famously advertised as a Fast and the Furious knock-off even though it's actually about a guy having a little bit of trouble expressing himself properly. And this has been going on forever: Back to the Future was actually marketed as a teen sex comedy, with the tagline "Are you telling me my mom has the hots for me?" and a teaser in which a woman with a husky voice asks Marty how far he's going.