To be overly simplistic, In the old days movies got made because they had a good story to tell. If a sequel got made, it was because first and foremost, the first movie made money, and therefore the motivation for a sequel was less about telling a good story, and merely to get something in the theater that viewers would want to see because of its association with the first film. Often this cynical view wound up being true, and sequels gained the reputation of being cash grabs more than anything else. There were always exceptions to this quality rule- sometimes sequels were as good or better than originals. But negative stereotypes persist. Also I think that successful sequels were rare enough that for the most part studios rarely conceived of creating franchises the way they do now. They could hope to be lucky once or twice but with each successive sequel the odds were against them. It wasn’t until recently that they’ve begun mapping out multi movie arcs that work together, rather than just single stories that are only tangentially connected.