I’ve been aware of two good reasons to stop when you see the stop sign open out on the side of a bus:
1. You don’t want to hit kids.
2. You don’t want people to think you’re an over-rushed weasel.

But I recently witnessed (at my daughter’s bus stop) a car drive past one of these stop signs and was shown another reason:

3. Bus drivers have radios at their disposal with which they can call in your license plate number. And as you drive by them, they are not moving, making it very easy for them to do so.