I follow people that post e.g. cat pictures, but I wouldn't buy their merch. I don't even know who these people are, really; their posts are a commodity to me. They're "oh, more cat pictures", not "a new post from [X]!" I found them through the app's recommendations, hit follow, and then never looked into them further. Why would I want to buy anything from them?
The edges connecting vertices on social networks have weights, despite the social networks themselves not modelling this. Some people, despite being very "connected" in theory, have a very low aggregate weight of connection; all their connections are barely there.
It's like having a million acquaintances and no friends.
(And, of course, some percentage of the vertices you're connected to might be deactivated/purchased/bots/etc. But even when that's not true, you still won't make sales on your "personal brand" to mere acquaintances.)