The money is there primarily because of high user growth. The 'Steemit' network effect is beginning to take hold, and speculators can see it growing further.
The key for Steemit’s success is arguably to reach a critical mass of active users, allowing it to take advantage of the network effect. Once that happens, everything else will likely become a self-fulfilling prophecy. The Steem Dollar becomes a relatively stable currency supported from multiple sources of demand and supplied by the Steemit printing press.