Cause people care about those characters at least, they have cultural cache already. On top of that, their comics have legendary stories and characters attached to them.
No one is seriously checking for Shang Chi, Eternals, Echo, Agatha, Marvels, etc. X-Men and Fantastic 4 have some of the most popular comic book characters in existence tied to them. If you want to revitalize the enthusiasm from fans bring in characters they already love, not try and get them to love completely obscure characters. They don’t have the main avengers to keep the lights on anymore
I keep thinking about Kang Dyansty and who are we even hype for to team up anymore? They need an injection of A-Tier characters agian