2. There is very little money in shorting. Pumping and dumping by making up positive news is much more lucrative. "to the moon" has been a trope for years, and there is no equivalent on the short side. Even the world's most successful short seller Jim Chanos was successful because the short portfolio functioned as a hedge that enabled a leveraged long position on broad indices. It's pretty hard make money net short when the market goes up for two straight decades.
3. The authorities don't have the resources nor the dogged inclination to hunt down fraudsters. The authorities can't and shouldn't base an exhaustive investigation on vaguely shifty CEO behavior. Short sellers can and do start their investigation based on gut feeling.