The scenario here is really bad weather COULD happen, and kids, parents or teachers COULD get injured/killed...
So the choices are ...
1) Cancel school and everyone can make their own decisions on how to stay safe,
or
2) "Force" people to go to school, and the District ends up the liable party to injuries and deaths.
Gotta remember who is making the decision - most likely an elected official who knows option 1 possibly results in a few pissy people who are inconvenienced to watch their kids, and option 2 possibly results in having to hold a press conference with 5,000 people at a candlelit vigil protesting a death(s) and calling for said elected official's job.