Hospital staff.

They’re not residents, you’re thinking of nursing homes. Roughly a third of hospital patients can walk without assistance, but yes. The rationale is staff doesn’t turn themselves into bullet sponges, because then who is left to remove the bullets once the shooter is dead? Either way, what do unarmed, untrained (to fight) people with the body armor equivalent of pajamas do to stop bullets?

The patient room doors don’t lock. Sometimes those doors are made of glass. But herding the patients who can walk into the halls is likely an opportunity for an active shooter to hit more targets. As such, everyone hunkers down, and the police take care of it. In theory, per the training modules. Police sometimes run drills with the hospital, depending on locale and interagency dealings.

Shutting all the fire doors is likely the only defense. Those nurses can be crafty on the fly, but there are limitations.

I can’t imagine a secondary piece of this policy isn’t hospitals avoiding liability regarding workplace injury/death lawsuits.

I just hadn’t known until now that in grasping for solutions schools found the standardized hospital policy and are running with it.