I don't believe the average person who uses a meta activity pub based social media will ever know about instances beyond theirs and the options to create accounts to get non meta social media. The service will feel no different from Instagram or Twitter and to them just be another site.

The benefit will be more for Facebook to try and entice instance owners to find more users to datamine, and try to influence development in a direction that starts putting them in greater control like Google did to Android.

I don't see this scenario of average people randomly seeking out independent non corporate instances to make accounts in and escape meta. Most are there because they enjoy the Meta experience and the large user base that all congregate there. Meta's only play in this is an attempt to expand their influence to those trying to escape them.