money duh. People love going ape for this tired premise, I guess. Right up there with killer dolls, cloned dinosaurs running amok, fast and furious, the umpteenth MCU movie you won’t be able to follow if you haven’t seen the dozen or so released before it, and boy we do not need another Aquaman sequel
hebspeaks 
Because they make money. I think they were far more frequent in the 1960 & 1970s though.
money duh. People love going ape for this tired premise, I guess. Right up there with killer dolls, cloned dinosaurs running amok, fast and furious, the umpteenth MCU movie you won’t be able to follow if you haven’t seen the dozen or so released before it, and boy we do not need another Aquaman sequel