I've known people (white collar) to call in sick because their days will expire, in places that have lax enforcement policies, so I'm not surprised that some workplaces get draconian especially if it causes someone else to get forced to work to provide coverage.
Sick days aren't part of your compensation, they are more like insurance. So of course they expire. I've had colleagues use a sick day for mental wellness. I've had colleagues use sick days while on vacation, ie food poisoning downroute. I've never had colleagues try and combine sick days with vacation days. That is considered a no-no.
