I guess porting is too expensive and a 80 million install base is more than enough to ensure a good profit. also, the hardcore fans of the games will even buy a PS3 to play it, so, why bother?
Wide spread releases make sense in wide spread appeal games, the niche stuff have always very loyal fans, like me buying a Xbox One to play Dead Rising 3 or wanting a WiiU to play ZombiU.

My grammar errors are justified by the fact that I am a brazilian living in Brazil. I am also very stupid.