I have heard a lot of stories about Koreans buying SBD or people buying it for tax reasons. All is BS.
Simplest conclusion is that a group of people, some gang, is manipulating it and laughing all the way to the bank. One of the evils of cryptos is the very easy manipulation. There is not enough in the system to keep this going but again there is nothing they can do. Perhaps F.B. or YouTube or whatever it may be, but someone is crashing the system. When a system allows payments as the one you mentioned then it is looting of the system as well. This whole steemit governance makes zero sense.
Were the small volumes on the SBD market an easy target for manipulation? That is my opinion anyways. If that's what happened it's too late to do anything about it and for some reason no one is talking about what we should do next or if it's even a problem.