Shorting requires perfect timing and trading skills. Shorting a highly volatile crypto market that is bullish is a recipe for financial disaster. Taking profits on big price spikes is ok though.
You don't perfect timing for it and trading skills. As long as you get some decent profit from that time, you can short at your will but sometimes the reason why a trader or investor stops to short.
It is because of the reason to aim for some more. And as that aim pursues to earn more, the time passes and that opportunity is being missed because of the market's volatility.