Turns out, other than piracy, there are no legitimate uses. The existing technologies are good enough.
P2P is cool if you have a desktop, but you cannot host from laptop or phone that spends most of the time sleeping (unless you want your battery to die real fast). The solution is hosting providers - which are already decentralized (and federated, if you squint hard enough)
Web of trust never took off - turns out people don't trust their friends' friends' much, some sort of centralized authority works much better.
_Cryptographic_ identities have huge problem of it's own - there are many people who don't have any persistent data on their PC - for example, they have only one laptop/phone, they don't back it up, and it breaks regularly. If your system requires one to keep a secret key for decades, it automatically excludes a very large fraction of computer users.
Publicly accessible versioning and immutable content sound cool for readers, but have very few upsides (and many downsides) for writers. And it's writers who select publishing technology.
People has been proposing those things forever. No one needed them back then, and no one needs them today. Just look at which decentralized social networks are actually winning (like Mastodon) - it's pretty much opposite to what's described in your comment.