I don't know.  How do you explain it?  Why did the price double in Oct-Nov after one year in the 220's, and why has it been parked in the 420's for the last  5 months?

But actually I can make up two excuses for the price not collapsing after the scam was closed. 

One: The MMM ponzi organizers and/or their victims are still holding the bitcoins that the victims bought in order to play the game.  The price will not drop back until those coins are put back in the market.

Two: It is a fact that other copycat ponzis appeared after MMM; and those copycats may have been more successful than  MMM itself, especially in China.  If that is the case, the price will not drop again until those ponzis collapse too.