Most people have been powering up their Steem.
What does that mean?
It means that well over 90% of the Steem in existence is not currently liquid. Though there is additional liquidity in the form of SBD (Steem Dollars), which are backed by one USD of Steem.
But that means that every week 1% of the SP is liquid for selling. If no one is converting to SP, then eventually it will all become STEEM which is debased 100% per annum and the curation will be dominated by the few remaining with SP.
It also appears to be a constant selling pressure juxtaposed against any speculation demand for STEEM. Analogous to miners divest BTC.
I see your point that the amount of STEEM available is only 10% of marketcap right now. So that can be another factor for price moving up so much.
Dan planned out the math of this pyramid scheme well. It is a front loaded pump with a long-tail die off.