a lot of shorts. As the price rises, they are forced to buy to cover and minimize losses. They made the original gamble, and in the case of these over-shorted stocks it was a bigger gamble. The only thing that could destroy the gamble is people buying the stock for higher prices than their short in high volumes and not selling (which would allow them to cover) until the price is high. If it's a ponzu scheme, it's on the people originally shorting to make easy money (wall street). Others may get losses if they chase late or hold too long.