“Why do they not have seat belts on school buses? Would that have saved any lives?”
I read once that they have assessed the risk:benefit of seat belts on school buses. The downside that mitigates the benefit is that the rescue of children in seat belts, especially when there is fire involved, is far more challenging and therefore in many instances seat belts might cost more lives.
That is indeed the argument. It is reviewed regularly. I will leave it up to the safety engineers to make the call. The soccer moms will always opt for what would have been desirable in the last accident, but that's not a good way to make policy.
Busses are considered inherently safe because of their size, weight, and large crumple zones. A head-on collision with a tractor-trailer or getting T-boned by a train or sailing off a mountain cliff will be bad in any vehicle, with or without seatbelts, but busses tend to be forgiving in most accidents. Getting out quickly in the event of fire is important.