Pretty much all the software mentioned is fully Open Source. And all the nodes are owned by different people or groups of people, and a lot of them are the kind of people who would never sell like that. And if they did, you could just move to a different node anyway. And Indieweb used to operate on the principle (probably still does, just haven't checked) that a standard wasn't a standard until several different pieces of software could work with it, not just one, so that ensures choice in the software market. Maybe in the future one node will become so overwhelmingly big and popular that they could be brought and it would be a problem, but at the moment there really is no one thing they could buy.