I was wondering about this as well. I really don't follow the MCU at all, but from my understanding the general timeframe and volume of content created is roughly equivalent to a TV series, and one that's more-or-less come to its finale with the latest film
The reason TV is rarely used for permanent fixtures in the park is that by its very nature it's tied to the zeitgeist of a particular moment in time. A film's popularity can ebb and flow over time as people discover new things about it or let it fade into their memory. A TV show's popularity needs to remain high in order to justify the ongoing production costs; when the popularity dies down or the story ends, the show is cancelled and generally forgotten.
[Edit: On the flipside, if a TV show continues ad infinitum, you run the risk of having an attraction that is completely out of date with the show's current content, and risks overlooking favorite moments, settings, and characters that could otherwise be incorporated. It would be akin to having something based on only Act II of a 5 act play. To an extent, this is also an issue with all of Disney's recent hyper-detailed franchise-based lands: Carsland and Pandora are set between the 1st and 2nd film of their respective franchises, while Galaxy's Edge is set during the 3rd trilogy.]
In the 64 year history of Disney parks, there have only been a handful of "permanent" attractions with roots in TV (Davy Crockett Frontier Museum, Gadget's Go-Coaster, Kim Possible/Agent P World Showcase Adventure), all of which lingered around well past their shows had ended and were forgotten by the general public (I'm excluding the Davy Crockett Explorer Canoes, since the connection is in name only). Heck, both overlays of the World Showcase interactive game began after the respective series had already been cancelled. Similar to the perennial Tomorrowland problem, as much as I'd like for Disney to keep current with their content for TV-related attractions, I recognize that's just not going to happen.
While it's current popularity is undeniable, I really question the wisdom of adding such a large and permanent area to the parks related to the MCU. From my understanding, End Game largely wrapped up the loose ends and sent the main characters on their way; will people still care about the Avengers in 10-15 years? Or will it be like having a major theme park area devoted to Lost, High School Musical, or Desperate Housewives?