In short, they've milked every bit of nostalgia you may have for their characters, I mean their properties, as long as humanly possible and then some.
I don't even have any nostalgia for these characters. They were a really fringe phenomenon in my country. But do you think that means we don't get the 20+ Marvel movies shoved down our throats? Oooh, no. We'll eat what we're served, or not go to the movies at all (that's the option I choose). If you wanted to make a parody of hamfisted, audience-contemptous cultural imperialism, you couldn't do better than Marvelwood.
Yes, everything in the movies/TV is derived from comic book. Comic books are extremely niche so movie content is new and novel to most movie viewers.
Multiverse / reboots / retcons also helped kill comic book popularity. It was a bad idea there as well! https://youtu.be/0PlwDbSYicM?si=iOlB2xYP8Cm1PwXc
> they've milked every bit of nostalgia you may have for their characters
No, it's not nostalgia. Marvel Film's greatest achievement is they took C and D tier characters and made them A tier. Iron Man was not super popular prior to the films. No one had even heard of Guardians of the Galaxy. Prior to the Marvel Cinematic Universe the most popular Marvel characters were Spider-Man and X-men. The film rights of whom had been previously sold to Sony and Fox.
In any case, I don't see how any of this makes them "shady". Not entertaining? Maybe. Shady? I honestly don't even know what that means in this context. Superhero movies strike me as extremely low on the scale of evil. Making mass market entertainment? Oh no the horror! /s