It wouldn't be it was/is a fad? In the 2000s there was literally a zombie movie coming out every week it seemed. In the UK there was load of movies about the UK "underworld" e.g. Football Hooligans, Drug Dealers, Gangstars and Illegal fights (Layer Cake, Snatch, Rock and Rolla, Green Street, Football factory, The Business and my favourite Sexy Beast).

There is generally a new film genre that does really well and people copy it chasing the money as people tend to want more initially until it is played out.