The problems are 2 fold:
People/kids don't want to put on a VR headset to play Roblox. I guess they're conceding this point by pivoting to mobile.
Meta is the opposite of cool. Real name requirements, only humanoid avatars, super corpo branding, etc really seriously hold them back from competing with VRChat or Roblox. This one is terminal it'll never be fixable as long as Meta is at the helm.