I think multiple things can be true at once. Grant is one of the most viewed content creators on YT in the golf space and sponsors want those eyeballs. That's the only reason he gets any attention at all from the PGAT and/or LIV. I can only presume, Grant would also want to stick to the space he knows best and has built a brand around. So, if he can't film content the way he wants to, why participate? He doesn't have anything to gain otherwise.
Grant played in the BMW Charity Pro-Am on the KFT a few weeks ago and was allowed to film the experience shot-by-shot. Which can be seen on his YT page. He was also -6 under par through 12 holes on his own ball before crashing back down to reality. He may not be PGAT good, but he can golf his ball. It's not like he's one of us hacking it around.
In short, sponsors want Grant, the PGAT has stipulations, Grant doesn't agree to the stipulations, so he doesn't play. Not really complicated I don't think.