Filecoin is live and being used, could you clarify what you mean? See eg Textile, Fleek, etc. It is currently storing ~20 PiB across ~1 million storage deals, according to https://storage.filecoin.io.
I read the Filecoin docs and it completely fails to explain the economic incentive. Can someone fill me in? Miners receive Filecoins as reward for storing people's data, who pay Filecoin to access their files. So... the only use for Filecoin is to gain storage access? Why would a miner, who by definition has storage, want a currency that can only buy more storage? Is there something else one can buy with Filecoin? According to Coinbase, Filecoins are "worth $50", meaning they can be traded for dollars?
People who want storage but don't have it must first buy Filecoin, which creates a market to exchange Filecoin to and from other (crypto or not) currencies. Miners sell their Filecoin on that market.