By the time they drop and being kicked out (if they do) the insiders already dumped their shares. Not to mention now all the index fund holders will rush to sell creating even more price pressure.

Shorting (itself being a bad idea for regular investors) also breaks the mantra of passive investing, 401k or otherwise. It’s almost impossible to short right after IPO because of low float and high margin risk.

These mega IPOs are just using passive investors as backstop.