CGI is to blame.
technology changed what movies are made & how they are made. Movies before CGI & after CGI are far different animals. everything 1993 & earlier was mostly dependent on a good story & good actors to make a blockbuster. With CGI, good stories & actors are completely unnecessary. Michael bay is living proof of that.
so if a hollywood exec has to choose between a good story that may or may not sell, or a crappy CGI flick that already sells & has a built in audience for the sequel, the decision is easy.
all of the CGI movies & their sequels could not even be made before 1993.
