No, it has nothing to do with the price of electricity, and diesel isn't cheap because the car is used on road as well as off road, so red diesel isn't an option. it's all about
1. Fitness for purpose - right now, there are no electric cars capable of doing what my diesel car has to do, or even of getting anywhere close to it. If all that I needed to do was to drive between one city street and another city street, then I could choose between diesel, petrol, hybrid or electric, but diesel is the only option available for a car that has to do heavy work. The only other option is a tractor, which not only creates far more pollution, it also damages the land because of it's weight.
2. Availability of resources - our farm is 9.5 miles from the nearest town, which has just one filling station that has just one charging point, so even if there was a suitable electric car, it wouldn't be practicable - and I think that it will be a very long time before this improves to the point that rural areas have enough infrastructure in place.