Grocery store workers don't spend 8 hours a day in a crowded room with kids who won't keep their PPE on, won't adequately wash their hands, want to give their teachers hugs / high fives, etc. Cashiers get to stand several feet away from those checking out, can put up plexiglass barriers, can slow down the checkout process a bit to sanitize between customers.

Hospitals are designed to prevent infectious disease spread. They plan for mass sanitation, employees wearing PPE, minimizing disease vectors. My wife's hospital has changed their policy to no outside visitors even on non-COVID floors. You can't do that in a school.

Don't get me wrong here, I'm not trying to downplay the sacrifice essential employees are making right now; they absolutely deserve hazard pay among so much else for putting themselves at risk for the benefit of everyone else. I asked my wife at the beginning of this if she wanted to quit, and we'd find a way to make it work, and she said "I'm a nurse, I signed up for this." That's just her mindset; she's been trained to work in a contagious environment and her hospital has many ways to help keep her safe. Asking teachers to take on that responsibility in addition to what we already ask of them, while being inside a petri dish of disease spreading is 100% irresponsible to everyone involved.