Their whole business model is fucked. They made some great franchises long ago and they are sticking to them while shitting on them. The problem the big two have is, first and foremost, that they are not sure whether they want the old audience or a new audience. Both want wildly different things, and by appeasing them both, they are achieving the opposite effect.
The old audience wants the classic Marvel comics. They have been following the Marvel Universe for quite some years and thus they know most of the stuff that's being referenced in the comics. They know the characters well, they know the lore well, and above all, they got accustomed to the "literary mechanics" and schemas their comics have always had, and change is logically frowned upo,. These people are probably adults who are huge fans of the brand who have an acceptable adquisitive power to buy several comics on their own, but the main problem is, their numbers are slowly going down because people either eventually move on or even die of old age. You can't expect to keep the same fanbase across the span of almost 50 years. Even though they are loyal, it's a good idea to secure a future for your company by expanding your target audience and bringing in new blood. Here's where the "new audience" comes in play.
The "new audience"'s only thing in common with each other is that they know down to nothing about the Marvel Universe. They definitely know the most iconic characters, maybe they have seen some of their movies, but overall, they know nothing about their world. Maybe they are just some kids who are just looking for some cool superhero comicd to read, or maybe they are some casuals who went to watch Deadpool expecting nothing and were greatly surprised to the point they want to read more. Thing is, they are not used to Marvel's quirks and just want to get into the stories without a huge entry barrier. But there is a huge entry barrier because they are expected to know about stuff that probably happened in now discontinued issues (it's extremely easy to find series with recently published 7th issues that no longer have 1st issues on sale). Fuck, the Marvel Universe is almost 50 years old, how the fuck can you expect them to keep up, even if most storylines are mostly but not entirely self-contained?
What can they do to attract these guys? Not all of them want the same. Kids probably wouldn't mind spare, self contained stories with no significant development, but teenagers and older probably expect some degree of plot to the stories. The only solution comes from clearing the state and rebooting the universe, which is something Marvel doesn't want to do, probably because it wold anger the old fans. Their solution to the dilemma is simply stupid, though. They don't want to lose "retrocompatibility" nor franchises, so they simply soft reboot heroes by putting new names behind them in hopes people see them as new superheroes where they can easily hook into, with traits they perceive to be "hip and cool" for the nee generations. This is retarded for many reasons: they anger the old fans, they destroy part of their brand depending on how deep the reboot is (how could you fucking tell Riri is Iron Man from looking at her?) and therefore old marketing and iconism, and they still haven't fixed the problems with the reluctancy of the new audience because the universe is still the same convoluted bullshit it used to be and following a superhero is a nightmare when every fucking comic is a crossover with funny and unintuitive naming schemes, and real plot progression is still hard when everything that was done in the past can be retconned with bullshit Deus Ex Machina time travel-tier stupidity.
The solution is simple, but risky: Marvel has to accept their old franchises must remain stagnant to appease the old fans and every absolute madman who wants to get into that clusterfuck, and thus the only way to seduce new readers is by creating new brands, and above all, new universes. Do apart with the "every superhero has to play in the same world as every other" and start thinking in terms of series. If a filthy weeaboo goes to a comic store and grabs One Piece from tome 1 to 85 they know they will get a tone consistent, lore consistent "self-contained" story about Luffy and his friends. No need to worry about the comic "The All-New Amazing Monkey D. Luffy", "The Marvelous Roronoa Zoro" where Luffy also appears from time to time and "The Straw Hat Pirates' Civil War", which is an edgy crossover in which all of them appear and fight each other (but never to permanent death because that would break the continuity of their other series). Don't want to read One Piece because you are looking for something more scifi? Grab World Trigger, and don't worry about having to track down anything else because it's not like Shonen Jump forced to write fanfictions of each other.