I feel like Hollywood doesn't GET the appeal of its own franchises and tend to tunnel in on specific names or even actors.
You gotta have an Enterprise in Star Trek, you gotta have Bill Murray in Ghostbusters, you gotta have a Skywalker in Star Wars, Bumblebee is the main character in Transformers, Dumbledore hijacks the Fantastic Beasts franchise etc... They never try to dig to the core elements that hooked audience that could work again if they dared to explore the world of a franchise beyond their tunnel.
I mean, trying to sell people in 1987 on a "next generation" of
Star Trek without Kirk, Spock, and McCoy was hard enough even giving the ship the same name, basically everyone would prefer a
Ghostbusters movie with Bill Murray than one without, and of the three non-animated
Transformers movies I've attempted to watch the Bumblebee spinoff was the only one I didn't regret wasting my time on. Star Wars became a dynastic saga from the moment Luke's parentage was revealed (given the veneer of Campbellian monomyth Lucas was going for, and that it set up Anakin's journey as the probable narrative for any prequels that might someday get made to complete this oddly numbered series), and I would further argue that it is the panoply of Star Wars media without Skywalkers following less directly related plots that marks any that do have Skywalkers as part of the "main narrative" of the franchise. The issue with the
Fantastic Beasts movies, it seems to me, is not shoehorning in Dumbledore
per se, but rather that Rawling generally seems to have lost interest in the characters she established in the first of those movies, and in anything charming or whimsical, and just wants to make Wizarding World political thrillers which nobody else wants.
Which is not to say that I don't agree with the basic premise that people doing revivals, remakes, and sequels often don't understand what really made the things work. I'd just add that some of the not-as-vital-as-they-seem things you point to have legitimate value in drawing audiences and convincing them that this is an integral sequel or whatever to bother seeing, that going back to the roots of why the original thing worked is fraught with perils because fans views of what the franchise should be have ossified over the course of time while their actual tastes and the tastes of the public at large may have shifted, and that sometimes the best thing is just to do something new with a franchise and throwing in Bill Murray or whatever may be the thing that gives you cover to do that, or that tacking on Bumblebee may be what secures funding and justifies Transformers branding for a perfectly fine, fundamentally unrelated movie about a girl and her space robot.
None of that, is of course, a defense of the
Fantastic Beasts sequels, which are just the most fundamentally misguided and baffling thing I've seen the original creator of a major franchise do with it. I watch one of those and leave it feeling a little bad about having ever complained about any
Star Wars movie.