I think this year’s majors put the handwriting on the wall for the PGA. They were betting they would stay better than LIV, that their players would be in better shape, and would out run LIV. With LIV getting multiple top 5s in each, and a win in 1 it showed that maybe not flogging your players can be good. Plus of course the PGA doesn’t run most of the majors. There were probably some behind the scenes discussions about shutting LIV players out, and the organizers of the majors said “nope”. Which all could put the PGA on a path to becoming the “small” league. We’ve seen the upstart league cycle in many sports, they generally come in addressing issues with the sport, often player pay, and the end game is either merge (NFL-AFL) or get replaced (British darts is a good example). I’ll give the PGA and DP credit for seeing how things were lining up and taking the merge path rather quickly.
The PGA was under immense pressure from PGA players who were the only ones who would lose big from further deterioration of the PGA. This was inevitable, but this isn't a true merger. I suspect it is agreement on allowing these leagues WGR status.