Although DCs like Crystal have less PFs active at any given time, there's still people doing them. I was hosting a Golbez EX PF a past weekend and it didn't take too long to fill up, we just saw a few familiar faces every time (which is fine actually, rapport is nice). There will always be people who don't want to DC travel to join a PF.

As an additional note that I don't think I've seen anyone mention (though I could've missed it): Open PF listings are not indicative of groups that have formed via PF and are actively entering and completing duties. Once they fill up they don't show up in PF anymore.