Mainly because a lot of the problems these guys are talking about just not materilaizing within the franchise have existed since like 2012.
Too many quips? Avengers 1, Dark World and Age of Ultron were infamous for this.
Every new movie is a sequel hook? Iron Man 2 was a 3 hour trailer for the Avengers, and this series popularized post credits scenes
Bad Special Effects? Phase 1 films looked like they were cooked up in about a week because their sets were so cheap.
Bad writing/Too much bait and switch? Remember how mad fans got over Iron Man 3 with the Mandarin twist?
I think all this discourse is less about Marvel "not being good anymore" and more about people starting to unconsciously realize that mindless corporate shlock isn't actually that gripping once you start holding it under the microscope. Like this series has been going for 16 years and hasn't actually changed, of course you're sick of it.
when they started to push movies everywhere, i knew that hollywood was getting out of ideas, now they just want to sell as much marvel plastic crap as much as they can (avengers OST was cool, tho)
yeah, the real turning point was when they moved away from the main characters (captain, thor, ironman, hulk to a lesser extent) and tried to replicate the same success with characters nobody had ever heard of and that pretty much only exist on paper as a footnote in a comic from 40 years ago.
yeah, maybe Robert Downey Junior as Iron Man could convince me to pirate your movie - but i ain't gonna be as excited for generic buff actor #8274 playing in a movie about the origins of the feared vigilante "the brown meerkat"