It’s not that film franchises didn’t exist before. You’ve got Superman, Batman, Shazam, Flash Gordon, Captain America, Dracula and Frankenstein serials back then. Let’s not also forget that films like Robocop and Swamp Thing also begat childrens’ cartoons. So there was media franchising before. Just not to the same extent we’re getting today.
It would be parsimonious to say that it took the mid to late 20th centuries to make film franchising an even bigger phenomenon than it was before. From then on we got Planet of the Apes, Star Wars (itself influenced by Flash Gordon and Dune, which also got a film adaptation and is getting another one now), Jaws, Terminator, Saw, Halloween, Child’s Play, Alien (and Predator), Annabelle, the current Marvel serials and Harry Potter.
Harry Potter would probably be the biggest film franchise relevant to this generation as they grew up with it one way or another. I never really read the books though I technically have one copy myself. But it’s got to be the biggest franchise that my generation grew up with. Popular enough to have other studios trying to buy the rights to adapting said book franchises like Twilight and the Hunger Games.
(Comes to think of it, Universal pretty much did the same thing when it came to riding off on Star Wars’s popularity by adapting its predecessor Dune though it didn’t go well as expected. Similar things could be said about Mortal Instruments.)
Twilight’s even influential enough to pre-empt another successful book turned film franchise, 50 Shades of Grey. That’s how influential Harry Potter is to this generation and somebody else’s gateway drug to fantastical literature. (I think Star Wars probably did similar things to it, itself being a gateway drug to Dune for some, including me.)
I don’t think Hollywood and its ilk will stop making franchises if one story went controversial or something. They’ve been doing this to prose books and comics for so long but because they’re safer to invest in as they already have established followings and conversely speaking, such adaptations help increase fanbases.
I swear even if a controversy were to rock one industry Hollywood pillages, Hollywood will co-opt another to make bank. As it has been before.