Prolific actors tend to also own their own production companies. Adam Sandler and Tom Cruise both own the production companies for their movies, which means they can have basically any role they want. Adam Sandler stars in dopey comedies set in on tropical islands with all of the same people because he likes getting paid to hang out with his friends in nice places.
Also, I think we can't discount how amazing plastic surgery is anymore. We don't see "old" actors hardy ever anymore. Even in the 90s, balding actors were pretty common, now you never see them. TC looks 35; same with Brad Pitt, Jennifer Aniston, Paul Rudd, etc. Why go with someone new when Brad Pitt looks just as young, but is a known quantity?