Can't think of anyone from, say, Game of Throne making it big after the show ended.
Same with music I feel like movies/shows are better off in term of new talent though
I think these are the two big things, and that they're basically all about franchises. Old stars are keeping their audiences and not retiring, all these old bands that are 60+ years old still heading out on tour. People know their brand and stick with it. For the record labels, etc, it's easier to keep promoting than try and build something new and there's more profit in that. For them, getting 70,000 people in a stadium at $£100 a go is much more desirable than building up someone new who may or may not get there. Once a band are big enough to sell out a stadium, it seems like a lot of them can keep doing it even with a 20 year break and no new songs (Guns N Roses have been on tour for a couple of YEARS just playing songs from the 80s/90s, same cities and stadiums, over and over and people keep coming out for it). They're probably expecting Ed Sheeran and Taylor swift to be doing stadium shows for the next 20+ years. Sounds like a good deal to keep that going as long as possible.
As for younger actors, as in Game Of Thrones*, the show is the star - not the actor. And that's the way the studios like it - they've put all the money into building a brand that people like, so all the promotion goes into keeping that going, not promoting actors who take all that value with them.
Even Tom Cruise, who is arguably the most famous actor working today doesn't make much that isn't a franchise. He makes Mission Impossible. If you take a look at his film list on Wikipedia over a ten year period, it's pretty stark how things have changed over his career. The most recent decade: it's Mission Impossible (Franchise), Jack Reacher (a sequel and a less successful attempt to build a franchise) Top Gun (Sequel) and The Mummy, an attempt to create a giant franchise universe of movies for Universal ...and that's it from 2015-2024. Aside from American Made, a genuine standalone movie.
If you think I'm cherry picking and "he's been making Mission impossible for 20 years! Take a look at how many movies 2005-2014 are franchises/sequels and standalone:
2 Mission impossibles, one Jack Reacher. 8 stand-alone movies. (didn't count the producer only credits).
If Tom Cruise can't get movies made (and remember he's the producer on Mission Impossible, so he could get things done), presumably few people can.
There's apparently no appetite for original ideas that can't be spun into giant franchises with hundreds of sequels. Not versus the Cinematic Universes.
*I hear that Jason Momoa has done alright post Game Of Thrones. ...As Aquaman. And some other films where he doesn't play Aquaman, perhaps. But mainly Aquaman