I buy Bitcoin to spend them at the hair saloon. I buy the bitcoins, my hair-dresser sells them it evens out the supply and demand and make the bitcoin act as a value token.
I have no place to spend steem dollars or any reason to buy them instead of Bitcoins for exchange medium purposes as Bitcoin is more proven. A 100% speculation driven demand can't last forever, there has to be a real demand for the token to use a medium of exchange or something else, in this case I had imagined there be sinks for it in various features on the sites but I can't really find any.