Simple supply and demand. Since hardfork 19 we have a lot more people selling on the open market, if supply is larger than demand the price will drop. Like a rock !

However, the SBD is meant to be a pegged asset, pegged to the USD. The USD is also dropping like a rock. Since the SBD has been trading over a dollar many witnesses have raised their BIAS to issue more SBD than steem when the 50 /50 payout is chosen.

My main concern for both the USD and the SBD is once it starts heading in one direction it's not easy to stop it....