There are 37 movies in the MCU - I think the general public is just over it.
The quality needed to stay consistent at a bare minimum or exceed expectations post Endgame to keep a following.
The quantity of content needed to stay the same at a maximum to make it feel special. The moment they decided to do Disney+ shows is when it trended towards becoming a forgettable IP.
The studio originally trained the audience that “everything is connected”, but they made the homework assignment manageable for general audiences by giving them 2-3 movies a year max to follow.
By adding in shows that were “take them or leave them” plus having both the films and shows quality waver and not be very inter-connected, this lack of interest was bound to happen.
Chapek and Feige misread the room. They thought they could replicate what came before but on a larger scale, yet not have their movies and shows intersect much at all for years until a Secret Wars type event. They needed to understand they caught lighting in a bottle with this original game plan. The originality of having all of these solo films play into one another in a mostly cohesive way but be entertaining in their own right is so difficult to pull off for over 20 films in 11 years. It’ll go down as a historical Hollywood moment where being in a Marvel film was like, what the cool actors do.
I think GA attrition was definitely going to happen regardless. But they needed to shake up the status quo to keep the fans more invested and they fumbled that hard.
I’m sure Doomsday and Secret Wars will make all the money because come on, it’s NOSTALGIA. Bringing back the primary Avengers, plus extended universe characters like the X-Men, Deadpool, other Spider-Men, etc.
But to many of your points, it reeks of desperation and a company that needs to squeeze every bit of profit out of sinking ship so shareholders aren’t pissed.