Because going electric is very expensive, probably requires some legislation depending on where the railway is.

For example there are many very short railways inside cities to access docks or industrial zones, those tracks have usually one or two trains a day, which is very low traffic, and can be located extremely close to housing. In that case it’s really complicated to electrify it.

The issue is, if you want to go electric, you need 100% electric, not 95. So it makes way more sense for freight to go diesel-electric like today