Gamblers can often bet large amounts out of the blue. That usually stems from the fact that a significant amount of money has just been lost gambling. So you could say that they are trying to recoup losses as quickly as possible. Should the Bitcoin once make a hard fall, for example with 50% in a week, a gambler can also consider this as such a loss and try to earn his money back by gambling. I don't know how gamblers would deal with it if the Bitcoin were to double in value, by the way.