We all know how the decision to make a sequel usually works:
Step 1: Release movie #1.
Step 2: Wait for box office returns to hit a certain level.
Step 3: Announce sequel.
Step 4: Figure out what sequel will be about.
The process is utilitarian. That's not to say it doesn't frequently work, but sequels practically become mandatory, at least within genre cinema, when the first part of a potential franchise crosses a certain money mark.