I'm not a hater of PF2, and I have gone on record with my bad experience of Roll20's integration of PF2. I have also sung the praises of PF2's implementation on Foundry VTT. But I will say this...Roll20 is well known to not be a good measure for Paizo products due to lack of support.
1) The user base of Roll20 is orders of magnitude larger than Foundry VTT.
2) Clearly, some PF2 players would want to use Roll20 (because it's all they know, they have already bought into the ecosystem, they are already familiar with it, etc.)
3) If PF2 was selling gangbusters, Roll20 would want some of that money and put more stuff on there.
4) And, actually, Roll20 IS putting most current PF2 stuff on there (at least significantly more than they had)
5) Foundry also has (I'm told) great support for 5e, Call of Cthulhu, and other systems. Why do we see those doing well on Roll20?