The problem is availability.
Because of the distribution model that everyone switched to in the 1990's you can only buy monthly comics as individual titles sold in dirty, windowless hole-in-the-wall stores that look as seedy and gloomy as porno shops.
Manga is available in brightly lit mall outlets where the employees wear clean uniforms and there are big windows so natural sunlight can get in.
There's also advertising, or the total absence of it. No, movies are not advertisements. The only other advertising that comics get is in the pages of other comics, continually trying to squeeze more money out of a predominantly aging and rapidly shrinking group of EXISTING customers.
Publishers need to hire serious marketers who can actually make the product appeal to new customers, and start selling in venues that don't look like the setting of an SVU Rape Scene.
Also, yes, the constant tangle of crossovers and shared continuity is a humongous turnoff. Every friend I've ever tried to get into a series, that's their first and biggest complaint. If they want to read a series, it's impossible to enjoy any one thing on its own because nothing exists on its own. It's impenetrable, and contributes to the whole "predominantly aging and rapidly shrinking customerbase" point.
The decline has been happening for years. Reforms should have started after the 90's bubble burst, but nothing happened. We're at a point now where a total collapse isn't about to occur, it's already happening.