Adaptations, particularly adaptations of novels, have always been a cornerstone of Hollywood filmmaking. There have always been remakes - if one considers them remakes - in the form of new adaptations of the same source material, whether a novel or a famous historical period or incident. Film series and sequels, on the other hand, with a few exceptions, like The Thin Man series, used to be largely relegated to low budget B movies, with most major stars considering sequels as beneath their stature. That started changing in the late 1960s and into the 1970s, and by the 1980s sequels were firmly established as another of Hollywood's big budget cornerstones.
Likewise, there used to be a few remakes of original scripts here and there, but they became far more prevalent from the 1990s onwards. Adaptations or remakes of old TV shows also started to become a staple from the 1990s onwards.
Of course even a lot of films based on original screenplays are very formulaic, and have been since very early on in Hollywood history, so they don't have all that much originality anyway (although formulaic films can still be very entertaining if made with wit and skill).
Hollywood does lean more heavily on the combination of adaptations, remakes, and sequels for its big budget fare these days than in its early decades. Personally I generally don't mind as long as the films in question are good, although I would like to see more adaptations of source material that's never been adapted before in lieu of some of the remakes.
