Playing devil's advocate, I think they're betting on the long game.
Eventually, when XR headsets become the size and have the practicality of sunglasses, they will become as ubiquitous as smartphones are today. It would be naive to think that the current smartphone design is the end-all-be-all of personal computing devices. We're already seeing small drops in smartphone sales worldwide, some of which are undoubtedly related to the global crisis, but let's be real: the design has hardly improved from the glass slab of the iPhone. We've lost bezels and the tech has seen iterative upgrades and small innovations, but in general it's a stagnated market with no clear path forward.
Current generations of XR headsets are still far away from mass adoption, but once the tech is drastically easier to adopt, possibly within the next decade, companies will flock to fulfill the demand, and Meta will already have an established platform.
That's their bet anyway, and while I dislike everything they stand for, I can't say they're wrong in this case. Facebook might be dying, but they're seeing the writing on the wall and trying to pivot to an—as of yet—nonexistent market.