Lots of idling. Lots of low RPM operation. Lots of stop and start wasting a lot of energy into the brakes.
A school bus is practically engineered to be an EV propaganda piece.
(Although, field trips?)
This lists the GVWR for the diesels at up to 36,200 lbs. https://en.wikipedia.org/wiki/Blue_Bird_All_American
This lists the GVWR for electrics at the same: https://assets.ctfassets.net/ucu418cgcnau/362sQcGinJzFxVqFh0...
Electrics also tend to benefit from better traction in crummy conditions because the batteries create a fixed, lower center of gravity.
Do note that the drive system for these EV buses is apparently built by Cummins. For Cummins to put the effort in, they see a reason.