IPFS doesn't work like that. It's not an immutable archive. A node on the network has to actively host (or "pin") the content for it to be available on the network. Yes the content can be cached by other nodes, but see the definition of a cache for why you can't rely on that in the long term.
Yes, I know, but I do think the theory is eventually, it would be cheapest and capable for permanent storage, well, storage is cheap already, the matter is more that the host is reliable enough, so it has to be decentralized.