The reserve requirements scale with both volatility and price. The clearing house needs enough money from you to be able to go buy those shares in the open mar

The reserve requirements scale with both volatility and price. The clearing house needs enough money from you to be able to go buy those shares in the open market 2 days from now if you vanish overnight tomorrow. If the stock is going up or down 2% a day, it's a lot easier to predict how much they would need than if it's going up or down 200% a day.