steem is created "out of nothing". The value of crypto isn't intrinsic it's based on what people are willing to pay for it. When you earn SBD it is essentially worthless, it's value is what the market is willing to pay for it.

Bitcoin isn't that different, you are creating money "out of nothing" too by mining. Nobody is putting in dollars so you can mine a Bitcoin or Ethereum. The value of these currencies is based entirely on what the going rate is.

If everybody decided tomorrow that bitcoin isn't worth anything at all, that's what it's worth. That is not different to Steem or any other crypto system.