Short-sellers are facing growing structural barriers in their quest to profit from share-price declines, a reversal of fortune that helps explain the heavy losses suffered recently by hedge funds that bet against Amazon, the internet retailer.

The hurdles for short-sellers range from the rise of private equity buyers, which are taking cheap or poorly managed companies out of the public markets, to the explosive growth of corporate share buy-backs, which are sapping liquidity and exaggerating price moves.