I think it’s because PR feels far more casual and easy to stick too and it’s something we all know very well, so it’s hard to break away from it, it also probably has something to do with the fact that Arma is very hard to run compared to PR being able to run on anything nowadays.
Although I agree, I would love to have a more diverse community, playing more Arma or Squad. Only doing events isn’t going to do that for us though unfortunately. We need the public un-modded Arma server to be something that will get players joining more! (cough, Invade and Annex), but that’s a whole different discussion