Could it be that the sales of PF 1 appeared so good because, in comparison to 4e, they were doing very well. However, 5e sales are so much greater than 4e's (or, let's be honest, any other E's for decades) that PF 2 doesn't look as spectacular as PF 1's did at the time?
IOW, could it be that PF 2 is selling about the same as PF 1 did, but, because the bar is so different now, it gives a completely different sense this time around?
On my preferred RPG site, RPGGeek, there seems to be zero interest in the new edition. There are a large number of PF1 PBFs currently running, with new games starting up every month. I think I've seen 1 PF2 PBF start up since it was released.
Of course, this is only one website and I'm not sure how PF1 was doing at this stage of its life cycle, but I'd be surprised if interest was as muted as it currently seems for the new edition. I mean, interest is pretty muted here too, isn't it? The 1e Paizo boards also seem more active than their 2e counterparts.