So why not a diesel hybrid?
Depends on how long you idle and how much you use your brakes. For highway driving the Diesel is much simpler. Around town? Hybrid makes more sense until batteries can store more energy per unit volume and mass.
If a Diesel already gets 40 to 50 mpg why bother with the expense and complexity of batteries and electric motors? All that stuff necessary to make a car a hybrid adds thousands to the cost (and the cost of environmental cleanup) during the life cycle of the car. In fact, you will never achieve payback over the lifetime of your electric hybrid.
“So why not a diesel hybrid?”
Every modern locomotive is such an animal.
THey haven’t figured out a good way to make diesels intant on-off capable. Hybrids turn the engines off when not needed and then turn them back on instantly when you press the accelerator down far.