Essential workers are not scarce. You need someone to do the job, but there is no shortage of qualified candidates. Hiring and training them is not a huge investment, and they are somewhat fungible. A department store could replace its entire staff within a week or two with no dip in productivity.

On the other hand, a few disgruntled knowledge workers can send a company into a death spiral if enough of them quit at once.

I guess companies don't care so much about their labourers, because there's an unlimited supply of them. Their skilled workers are perceived as an investment, because they're expensive to replace and shape the direction a company takes.