It's not that simple. Lots of people connect a Quest to their PC. Steam VR hardware surveys show that Quest accounts for more than 50% of headsets used with Steam VR.

Developers were starving before standalone. Only a select few games were successful. Now many devs have millions of dollars of revenue from their apps on Quest.

If they didn't have access to an exploding ecosystem like Quest provided, there's no doubt many devs wouldn't still be in the VR space, and instead working on a more lucrative platform. I have seen many interviews of VR devs saying exactly this.

So yes, now most devs are naturally not going to target a platform which provides 10/20+ times fewer sales. But even still, there's certainly more headsets on Steam due to Quest.