The reason I believe sequels are doing good is:
- movie theaters have been perverted into massive and expensive hype fests
- in strong opposition, past movie theaters were not expensive to go to and got you entertained in a social setting
- due to the rise of large chains, small and cheaper theaters have died out.
- assumption: the price to rent a movie for your theater will probably be horrendous by now
- sequels have kind of a known quality which lowers the hurdle
- that means new movies could be watched in smaller theaters and would have to be sustainable for those