I saw a movie a few weeks ago called Unsane which Matt Damon played a small cameo as a detective advise the main character who was a victim of a stalker. Only a few minutes but he was easily recognizable even in a pretty cheap looking movie (I enjoyed it but it was filmed on an Iphone).
I guess Damon has a nice reputation as a easy to reach, easy to work with kind of guy. He comes across a likeable guy. Which builds up a lot of friends/connections. Maybe from there him popping up a lot in cameos is just a bit of fun for him and all you have to do is ask.
Matt Damon may be the king of the uncredited cameo, but I swear there was a period from 2012-2019 (? maybe it’s still going on) where every TV comedy would have a one-shot appearance by Fred Armisen.
I’m sure he gets paid plenty for his starring roles. But a starring role is different from popping in for five minutes of work on a lark. He probably does the cameos because he finds it fun. Plenty of successful people have worse hobbies.
But doesn’t a Matt Damon cameo immediately take every single viewer out of the movie as they think "Hey, isn’t that… is that Matt Damon? Yeah, it’s Matt Damon. Huh, wonder how they got him to be in a movie like this? Are he and the director old college pals, or on the same bowling team? ‘Mark it zero, Matty!’ I’ll have to look that up when I get home, maybe I should just pull my phone out now and google it, I mean, I’ve completely lost the plot by now…"