While the rise of Superhero movies has been all the rage, the slide in gangster genre had declined. However, there is no correlation between the two. A lack of good story telling, too large of budgets, and release dates have hurt the crime movie business. Black Mass was a mild success I believe due to the fact of the intrigue of Johnny Depp transformation and acting.
The biggest reason certain genres fad away? The audience gets younger and simply not interested in the historical perspective. Also, how many ways can you tell the same story? That's what makes suoer hero movies interesting. Let's put aside for a moment, the big budgets, the world renowned actors, and the huge marketing budgets, superhero movies are interesting, complicatedcomplicated, and fun. They also posses a certain family value. You can take for the most part the entire family. Crime is crime. You can't always take your eight year to see crime drama.
In short, the Super power in super hero's is that they make us believe we can be, heroes too!