8 Reasons Hollywood Will Never Stop Making Sequels
2. They're A Proven Money-Spinner Because Just Being A Sequel IS A USP
At the end of the day, sequels work. That's why we get them: people will go see them. And even when we get a run of lacklustre follow-ups that fail to set to box office alight - see recent triple-whammy of Alice Through The Looking Glass, Teenage Mutant Ninja Turtles: Out Of The Shadows and Independence Day: Resurgence - there's always a whole host of successful sequels - Captain America: Civil War, Finding Dory - to show it's something about those particular movies, not the nature of the sequel in general, that's at fault (this is what the stats in the first point really attested to).
Sequels can work. And if something can work it's a safer bet than something that just might work. If you're a movie executive and a producer comes to you with two identical movie pitches, except one is part of a pre-existing series and the other a completely original pitch, they'll go for the former every time (this can be extrapolated for adaptations of books, games, TV shows et al), because it's proven to make money. The selling point is that it's a sequel.
Even big budget movies that are "original" come with a hook like that, usually a named actor or director; of those seven non-franchise movies from recent years, only two aren't part of a pre-existing brand. And that's because brand is the word of the day...