Well, I think that would be the "promising attach rates" bit.
My issue was using "strong sales" as a differentiator which justifies developing for PC VR rather than PSVR. My understanding is that PSVR has sold rather well, given its supply constraints. If hardware sales are a factor I would have thought that PSVR would be on equal footing with Vive and OR, at least.
It probably is a combination of a bunch of factors. Attach rate, dev costs, closed hardware vs open hardware etc.
PSVR definitely sold more than the other VR systems according to some sources, but that doesn't mean that the games all sell better. Especially since we're at the infancy of VR, most games are niche indie games. Games that historically sell more on PC.