I cannot speak for PG Music, but I suspect that part of the issue (pre-COVID) has been that there a quite a few session musicians who aren't keen on the idea of work-for-hire projects. By way of example, in the past, I would routinely try to hire certain session musicians in Nashville for demo sessions - certain guys (Brent Mason as an example) simply wouldn't play on demo sessions, they would only take master session bookings, and often demanded double or triple scale. That of course was when session work was plentiful and we were printing money in the country market.
I would think with the current COVID anchor around the industry's neck, that more players would be willing to take the work-for-hire sessions than in the past.

http://www.rogerbrownsongs.com
http://www.nashvillesongwriters.com/roger-brown