1) The idea of a set of reusable APIs around data ownership could actually be the foundation of a new internet. If it becomes impossible to concentrate data, the system will be more resistant.
2) The appeal of the Internet lies in the services that are available to users. A decentralized system doesn't appeal to capitalism, value is best captured through centralization and intermediation. Capitalist enterprises produce the bulk of services at the moment. This is a major adoption hurdle.
3) Dr. Berners-Lee appears to be a (digital) anarchist at heart, and it's a painfully beautiful vision.
4) He is partnering with capitalists to try to achieve an anarchist vision. This is a contradiction in terms. Capitalism is about competition for the working class (i.e. users), domination and centralization.
5) It sounds like what he wants is a more egalitarian and democratic system. He might want to talk to more radical political theorists (I assume he may have already in the decades he's been kicking around).
I wish Dr. Berners-Lee the best. I hope Solid gets some adoption. I've heard some people are using Mastodon. Here's hoping it's a trend. Nonetheless, if enough people start migrating, the corporations will offer them something to come back. After all, they can afford to, tech profits in established companies are obscene.