Facebook/ten cent/etc have literally zero reason to stay off the play store. Google encourages them to be malware, and doesnt curtail their bad behavior is any way.

Apple doesn't. They might not leave while they think they can also destroy the security of iOS in the US, but it is a complete and utter certainty that the literal day any similar law takes effect in the US that Facebook and all their apps leave the App Store completely. They absolutely can trivially walk people through the steps from their website and the apps that are already installed, and they already have the monopoly to force their users to deal with it.

Apple isn't Reddit, building a market by claiming to be open then locking it down. They built their market because the walled garden is a massively better product.