In short: Apple has made a fully realized spatial operating system, while Meta has made an app launcher for immersive Unity/Unreal apps for vanilla Android. You can get away with an app launcher when all you want to support is fully immersive apps that don't talk to each other. But that fails completely if you are trying to build a true operating system.
Think about what has to exist, to say, intelligently copy and paste parts of a 3D object made by one application into a 3D object made by another, the same way you would copy a flat image from photoshop into a Word document. The operating system has to truly understand 3D concepts internally. Meta is building these features but it is stuck in a really weird space trying to wedge them in between Android underneath and Unity/Unreal at the application layer. Apple has had the advantage of green field engineering it exactly how they want it to be from the ground up.