The most likely explanation is here [1]. Pilots (and apparently some air traffic controllers) are doing a sickout to protest vaccine mandates, presumably to make the powers that be understand just how difficult they can make things for the country if they proceed with intended mass firings. But the sickout is technically illegal, so nobody will acknowledge it. That is why you won't see a clear explanation of this incident - probably ever. You've never seen anything like it because we have never been in a situation where a significant percentage of the population is being threatened with the loss of their livelihood unless they take something that many consider to be quite dangerous.
[1] https://news.ycombinator.com/item?id=28824370
Edit: deleted link to tweet, comment below points out that it was from a suspect Twitter account.