Those admins are unpaid?

Managing a store it’s a LOT of work. And you are doing to provide profit for other people. Who is going to do it for free?

It’s not like social media where people may volunteer to admin and mod, and users may donate because it’s a common goal of share information, opinions, knowledge, funny stuff etc.

Here we are talking about bussiness that do what they do because they want money. I would not volunteer to admin a store so shop owners could earn money, that’s for sure.

And I still not see the advantage of doing within the ActivityPub instead of just being a normal service where all interested shops could join.