As far as I'm concerned, the World Pool Masters, World Cup of Pool, Premiere League Pool, Mosconi Cup, and Reyes Cup are absolutely exhibitions / invitational events. Matchroom might have a merit-based selection process in effect but they fully reserve the right revoke an invitation.
Molina Mike shared a take that I hadn't heard said before and it really goes beyond the typical politics and PR backlash takes I've seen. When you get an invitation to something as prestigious as the Mosconi Cup or the Reyes Cup, you sign up to be part of a production machine. There's a lot that goes on in the promotion of the event beyond just showing up the day of with a stick and playing. There's an expectation you'll show up for the photo shoots, interviews, press conferences, and the majors leading up to the event. If it's not an explicit contractual obligation, it's certainly a cause for the promoter to consider swapping you out for someone that will participate in the build up.
That concept certainly resonates with what you might expect from other sports. Even think of what Albin said in terms of being an "Ambassador" and "Co Promoter" of Predator and Predator Events, he has obligations to fulfill.