I personally know of several pilots who are using up their sick time in anticipation of a showdown over the vaccine mandates.

Southwest has been running with a pretty shallow pool of pilots for some time, and COVID made the problem a lot worse. Furthermore pilots who opted (or were opted) to idle have to be re-certified before they can rejoin the pool of active pilots and training is overwhelmed and backed up.

Juan Browne does a much better job than my ham fisted attempt - and a WAY better job of going into detail than this superficial article too: https://www.youtube.com/watch?v=kO39nIcuPhQ

BTW he is an active commercial pilot so he knows a bit of which he speaks and isn't just scraping content from elsewhere and resummarizing.