It's not "but blockchain" so much as avoiding either logistical or trust dependency on a single entity. Blockchain has all sorts of problems and limitations, the idea of a working currency based on it is absolutely insane IMO, but it has these particular properties. So do more complex systems such as IPFS or Tahoe-LAFS or LOCKSS, but ... well, they're more complex. Other solutions such as simple mirroring don't necessarily solve the trust problem. Of the technologies currently available, blockchain seems like a pretty decent choice.