Actually not relying on one is more portable across isolated networks, and requires way less computing resources. Plus, blockchains are usually a privacy issue.

I'm highly interested in the topics of decentralized (federated or distributed) platforms and identities, but I don't see what a single blockchain brings to the table? I could see profiles-as-blockchains, though, or instances-as-blockchains. But the rationale isn't clearly explained in the website, so it feels more of a buzzword and less of something that efficiently solves an issue (content discovery and global indexing, I guess).

Lastly, would you mind stating your affiliation? Thanks :)

They are attempting to decentralize and distribute video encode/delivery, and a big piece of that is a poof of work implementation to incentivize and reward reliable nodes.

Just one example, but there are others, and a lot of progress has been made to reduce the strain caused by throwing crypto into something that fundamentally needs to be very fast and lightweight to be usable.

Edit: Corrected duplicate links