Anything from lack of interest, fear of cryptocurrency regulations, focus on bitcoin over other altcoins, competition, market manipulation from big players in the market, whales selling off, steem also produces more tokens every day by the nature of how it's designed so there is an element of deflation as the supply increase if you sit idly by and don't keep up with your earnings. There are so many factors to consider. Eventually it will go back up though, everything has peaks and valley and we've seen steem low like this before and we've seen instances where SBD prices over took STEEM only for STEEM to later recover so stay patient and wait it out.