Why? Because they make Godot available on as many platforms as possible? Isn't that core to the idea of open source?
I think you misunderstood the announcement. The fact that you can now download Godot from the Meta store doesn't mean Meta has any influence on Godot, or that they could change the projects direction. There are plenty of other ways of installing Godot, too.
I recommend reading this toot (by a Godot maintainer) for reference:
https://mastodon.gamedev.place/@akien/113180320567155590
@cjr @godotengine
wasn't reacting to the availability part. rather...
"This means you can develop games right on your headset without the need for an external computer"
gives meta some more power.