I really first started noticing this during highschool with the whole buffy the vampire slayer. What's really sticking out to me now is the whole "evil hero" character. Angel from the show angel, Constantine, the entire Twilight thing, Grimm (which has a human hero but lots of "monster" supporting roles, Supernatural which has many "evil" characters doing good and Angels being very evil, Disney gets in on it with movies like Hotel Transylvania, etc, etc... Ironically enough "PC" has crossed the monster barrier as well and now monsters aren't really bad they're just misunderstood.
Were a a tinfoil hat type of person I'd postulate that hollywood is run by demons and this is part of their slow integration process. Phase one was creating fictional facsimiles of various monsters, phase two is showing how they really aren't that bad, stage three is a further humanization of monsters into heros, stage 4 will be a global "unveiling".