It's how they make money, it's how they gauge success, it's how and why they do everything they do. And in today's marketplace, the more movies you can make out of a single property, the better. Why just have one Twilight: Breaking Dawn film when you can split it in two? Why even settle for just a potential Dracula trilogy when you can play the long-game and have Dracula sequels, spin-offs, and reboots for decades to come?
The easiest and most common way that studios profit off of this is turning one film into a setup for another film. Rather than using the idea they have for the film they're making, they make a film building up to that idea so that they get two films and audiences get more movie. Everybody wins, right?
Well, not when that setup film winds up being little more than a two-hour trailer for what is to come. Whether it be belated sequels attempting to get audiences back onboard for future adventures or misplaced attempts at kickstarting shared universes, these are the films that cheated audiences out of what they wanted to see in the first place.