Everybody hates sequels when they sit down and think about it. But, when they don't... When it's "Eh... Let's go see a movie. What's playing?" They are faced with two investment choices: One selection of high-risk, unknown, unproven, original movies Vs. another selection of low-risk, familiar, proven productions --some of which are well-known to be liked by their group and others are well-understood to be skippable.
The "Eh... Let's go to a movie" scenario makes up a far larger portion of the total revenue than the carefully researched, highly anticipating planners. It should be no surprise that they spend so much on sequels and adaptations.