I think you are thinking about this in the wrong terms. You might as well ask where the bitcoins come from. Any cryptocurrency has a valuation based on several factors - the total amount of coins in circulation, the total market cap, whether the number of coins in circulation is capped or inflating, and of course (most importantly) how much people are willing to spend on the coin. It matters very little where the coins come from, provided that whatever mechanisms the blockchain in question uses to ensure the security of the network are strong enough. Using the most famous example of Bitcoin, a "proof of work" model is used, requiring tremendous expenditure of processing power to crunch the complicated math problems necessary to mine the next block added to the blockchain - and of course a system of transaction verification that requires multiple independent actors, unlikely to collude with each other, to verify new transactions into the blockchain. This system has worked well so far, the Bitcoin blockchain has been relatively secure, no one has figured out how to hack it and generate coins out of nothing, and so the value of bitcoin comes both simply as a store of value ( as a rare commodity, like gold - you can't just go make more gold out of thin air, you have to put the work in to dig it up, exactly parallel to bitcoin) and a secure, non-falsifiable, non-censorable way to send payments worldwide. Steem is very similar but does not use a "proof of work" concept. Instead of miners running server farms, Steem has witnesses running server nodes. This is what produces the new coins. What prevents anyone from just making more coins is first the work necessary within the social media network to gain enough Witness votes to become a top witness and receive a payout from running a node; and second the verification of new blocks by randomly selected and unlikely to collude groups of witnesses. In essence, it is the activity of the social media network itself that generates the security of the Steem blockchain. The more users there are, the harder it becomes to be a top 20 Witness. As long as the Steem network is secure and new coins are being generated according to the inflationary principles hard coded in to the blockchain, Steem has value in similar way to Bitcoin as both a store of value and (more importantly in this case, because it actually beats the pants off Bitcoin here) as a method of sending payments worldwide with zero fees and extremely fast transaction times. Take a look at your other options for sending money around worldwide. Try to do it through your bank or by wiring money and tell me if you see any value in something that lets you do it for free, and in a manner that is 100% not falsifiable, and is public record :)

Much love - Carl