There is plenty of evidence to suggest otherwise, decentralised or federated versions of all kinds of things on the web exist, and work, today... Just no one uses them of course.
The problem is none of these ideas seem to be able to obtain dominance, because that's not in their nature, that is in the nature of capitalism at the deep end, and it already has a grasp on the things that most decentralised tech is trying to replace.
The exceptions are decentralised tech that has no corporate competition, e.g bittorrent. I think that's a very useful observation, it's a classic "make a better horse" scenario, it's difficult to see the future when you are focused on present technology - I think the way to make the centralised web obsolete is not to merely decentralise the existing manifestation of it, but to make something entirely, fundamentally different, because corporations don't innovate in that dimension, so they can't compete, and can't dominate early enough to monopolize it.