Because there's no point as they need their apps to be cross platform and so Apple is setting a baseline for what behaviour is allowed.
But once Meta, Epic etc can run their own stores on both iOS and Android they will absolutely move their apps to them. Epic has already said how important this is to be able to implement their metaverse strategy.
Epic already did this at the height of fortnite's popularity, by using a "fortnight installer" app that you had to get from outside the play store. Can't remember why they backtracked, or why they didn't offer store/sideload versions at the same time.
Google even took steps to prevent people from installing malware pretending to be fortnite, and steered them to the official installer. Not out of the goodness of their heart, TBF.
I really, really don't think it'll be as easy you as say. Neither the audience nor the regulators will let them off easy, and these creaking giants aren't exactly great at launching popular new platforms, these days:
But once Meta, Epic etc can run their own stores on both iOS and Android they will absolutely move their apps to them. Epic has already said how important this is to be able to implement their metaverse strategy.