[freeflight]

Those are very specialized vehicles, that's most likely the reason they haven't been electrified yet, that will probably only happen as they age too much and can't be maintained anymore, mandating a complete, more modern replacement.

I also doubt they make up a substantial part of the rail traffic, if we go about it that way we there's a whole bunch of vehicles with horrible CO2 emissions that only have gotten barely viable electric alternatives in the last handful of years, like excavators, bulldozers and all kinds of other construction/hauling/maintenance vehicles.