> I pay a monthly fee to a business for my mail server, and I chose a business that makes data privacy a top selling point.

And you're free to pick a mastodon instance that offers the same (if that's something you cared to do). Do you also complain that it's possible for any rando can spin up their own email server and start passing out free email addresses?

Your perspective on "empty calories" social engagement is very narrow in my opinion, because you seem to equate all social interactions by the measure of existing, objectively bad, services. I think that over time the rise of small indie servers that will work on a social graph but in a similar way to email, will prove that "meaningful" social networks can exist, and my personal hope is that they won't be focusing on monetization. I don't see any reason why companies won't be able to build on that and offer you the same guarantees about your data that your email company gives you.