There are blockchains which do that now, but for fragmentation they rely on users of the blockchain to help by storing parts of files on their computers, for example. They then get some remuneration when files are retrieved.

Steemit is different. There are mainly just witnesses, as I understand it. There are other nodes as well, but they are just that, "other', and do not form the backbone of the system. I don't know how correct I am in this, but I do know that developing a big network for the readily accessibility of large amounts of data is a big task, and is not just a case of an add-on.