It's the nature of movie making as a business for any even vaguely successful project rapidly to be considered for its franchise potential. It doesn't matter if the story ended pretty conclusively with the world saved and the hero dead after a noble sacrifice, once those millions start rolling in the studio suits will start thinking "sequel?"
Often it is only the objection of the original movie's star that prevents some truly terrible sequel concepts from coming to fruition.
The Se7en sequel, Ei8ht, in which Morgan Freeman's Detective Somerset developed psychic powers to track a new killer? Shot down by Freeman. The Forrest Gump follow-up in which Forrest hangs with Jenny's ghost, captures Saddam Hussein and brings down the Berlin Wall? Rejected by Tom Hanks as no longer relevant post-9/11.
There are, however, those rarer cases when it isn't the star that's holding the sequel back at all. In fact, the lead actor seems keen to throw themselves into returning to one of their signature roles with a truly bonkers new instalment and it's only the sheer weirdness of the pitch that is preventing a studio from committing to it too.
But, hey, if the stars are happy to commit themselves to such outlandish concepts as these ten crazy sequels, shouldn't we perhaps get a chance to see them?