Liability. Pure and simple.
The inconsitency is because the superintendent largely looks at each event individually.
My first job doing construction adminstration for my architecture firm was with jenkins independent schools for a renovation of all of their facilities. I used to sit and BS with the superintendent for about an hour after giving him an update on construction progress. During the winter phase of that project he would basically be sitting in his office fretting over whether or not to call school. He told me, "listen, crazy... If i call school and there's no reason, i have parents bitching at me for a month because it throws their entire schedule into whack because they have to find someone to watch their kids. If I don't call school and It's awful, I have parents bitching at me for a month because i have put their precious angel's life in jeopardy. If I don't call school and It's bad, half thr kids won't come and we'll lose funding. If we're in school in the summer, no one is happy."
They had every monday off from january to march as built in snow make up days.