The theory I've heard along those lines is that he lost the Bitcoins years ago due to incompetence and was trying to make back the losses so that he wouldn't have to own up to it. You can imagine how that strategy might have spiraled out of control as the price of Bitcoins increased.

It's mostly speculation. But nearly everything we know at this point is speculation, other than that Karpeles has a history of both technical and ethical shortcomings, which basically means that anything is possible.