I think there’s something to the big-universe effect.
I’ve read mainly DC since I was a kid, with more indie books mixed in over the last decade, and only the occasional Marvel book. What kept me coming back to DC was the familiar universe. What’s kept me away from Marvel, I think, is the unfamiliar universe.
I’m a lot more willing to pick up an indie book that takes place in its own self-contained world than a book in a big established world that’s likely to pull in the rest of the line. This has been true for Marvel, certainly, but also for WildStorm (when it was its own universe), Top Cow, etc. The books I’ve read from those publishers, Marvel included, tend to be creator-driven or take place in their own little corner of the shared universe.
TLDR: I think Marvel’s fine, but I’ve just never gotten into it.