Apple has absolutely cornered the mobile market, so that’s probably why they don’t seem to be in any hurry to seriously support the PC gaming space.
They tend to focus hard on niches they can overcome, and PC/console gaming is a little too established for them to stick their toes in. They tried with the Pippin and the pre-Halo era of gaming, but it didn’t work out for them.
If the Apple headset takes off, they may start pushing harder for VR game support, but who knows?
Mobile game devs are making their games with iOS in mind, because iPhone users are more likely to pay.