I assume Facebook's objective is to get people to adopt Facebook accounts for VR use.
They can do it two ways, sell to people who are looking for a stand-alone experience provided there are decent apps available with no PC requirement, and they can do it by selling to PCVR users who want to use it that way.
Both ways necessitate Facebook accounts (for the Quest) so both ways work from their point of view. I don't see why they wouldn't want to carry on with both routes to be honest.
There may be a few people who only use Quests for PCVR but I'd guess they were in a small minority, Most people who bought a Quest for PC use are going to also try out the stand-alone features, Steam would seem to be a decent enough vehicle for Oculus so is definitely of interest.
You've also got to remember that anyone using Oculus-Link to play PC VR games has the Rift Store in their face as soon as they press the Link button so the first port of call is going to be the Rift Store when it comes to buying PC VR games.
And like I've said above developers are still using the Rift Store to launch their games so the Rift platform isn't as dead as SOME PEOPLE would like it to be.