That would be because they're lying. Not the guy in the meme. Companies are constantly saying they're short of workers without actually hiring more. There's several reasons for it, but mostly it's to influence regulation on training and safety standards. In teachers it's a political preference for private schools at the expense of the normal school system.

We produce enough nurses, pilots, and teachers. But the shortage myth justifies running skeleton crews, treating them badly, and hand waives high turnover.