How many actors?

RDJ - money

the others - their first role was small and they came back for a larger role

If you think the MCU is bad for reusing actors, just waiting until you hear about Doctor Who, especially Classic Who

They don’t keep going back to the same actors. They just have done it a few times and you’re hyper focusing on it for some reason.

"Actors cast in movies" feels like a fork in kitchen situation

There’s also smaller castings that break continuity like John Benjamin Hickey playing Peter Lyonne in Jessica Jones and returned in Daredevil Born Again as District Attorney Benjamin Hochberg.

And Andrew Polk who played Colonel Morty Bennett in Punisher S1 and also returned in Daredevil Born Again as Judge Jerry Cooper.

Both of them didn’t have good fates in both of their Netflix shows and it feels weird to have them back as different characters knowing what happened to their previous characters. We can suspend disbelief only so far.

RDJ for fanservice and money

Ebon and Mahershala, remember they were cast before Disney decided to embrace the Netflix shows as canon, plus Mahershala wanted to play Blade, word is that he went straight to Marvel wanting to do Blade despite already playing Cottonmouth, plus Cottonmouth is dead and Micro story is wrapped up so i don't see the harm in giving them new roles, plus Ebon is playing a character from another universe and Deadpool 3 established that it is possible to have characters from other universes resemble characters from the Sacred Timeline

Gemma Chan, its been said its because Marvel wanted to give her a more important role in the MCU given how her character in Captain Marvel was so small, plus she's in heavy make up in Captain Marvel so one won't know is the same actress at first glance