Only because they've been in the MCU.
Who was Chris Evans before the MCU? Hemsworth? Ruffalo? Tom Holland? Practically nobodies until they signed on with Marvel.
Cooper and Diesel are outliers - not the constants.
As we can see with Robert California, Ego, Hela, etc, they've kinda been casting big-names for villains already.
What this means - is - I think groups like FF and X-Men are going to feature relatively unknown people. Maybe John Krasinski isn't being considered for Mister Fantastic. I wouldn't say he's a "big name" in movies, but he was for 1 long-time TV show.