It is always a surprise when a series will remove a character for a sequel movie. Sometimes this can be due to a rift between director and actor, or because of scheduling conflicts. It's somewhat to be expected.
Sometimes though, a character will cause so much animosity in fans that when it comes time to create the sequels, writers and directors will simply leave them out entirely, saying they are off elsewhere during the film or killing them offscreen between movies.
This can often be just what a movie series needs to claw back to success and sometimes it can be the last-ditch attempt to save a failing franchise.
Some characters simply don't fit in, or irritate fans, or are just plain dull. There are some that are removed because the general public sees them as offensive. Whatever the reason, the removal of a character from a franchise tends to be due to an idea that were they to remain, they would annoy fans so much that they just wouldn't see the movie.
Whatever the reason, these characters were enough of a problem to fans that studios and directors deemed fit that they should be removed, for the sake of the franchise as a whole.