You are right about one thing, Amybear. You ARE way off the mark.
Throughout all of my time at school, there was one assembly which stood out in my mind, and still does over 30 years after leaving the school. I was in my first year of secondary school (year 7 today). I was just a few weeks into my first term there and it was Monday morning.
I remember our school headmaster, dressed all in black and barely able to get his words out. The serving deputy head, his friend, friend of most of the staff and well liked by many pupils too, had died of a sudden and massive heart attack that weekend. As others have said, schools are communities. The sense of shock throughout our school was palpable. It was a very shocking event. I am sure it would be at least as shocking, if not more so, had a child of my own age died.
The deputy head's funeral was just over a week later, in the afternoon. School closed at lunchtime to allow staff and pupils who wished to attend to do so. It was absolutely right that it should have been so.
Teachers build up relationships with their students. Professional relationships, but usually cordial and caring nonetheless. Many of them also have children of their own, perhaps of the same or similar age, and they cannot fail to be affected by the death of a child they have taught regularly. They are human. They can be upset and shocked too and want to pay respects however they can.