I've wondered that too (especially as the owner of a diesel car). My best guess is that hybrid drivetrains come at a price premium compared to plain gasoline engines and Diesels also come at a price premium compared to plain gasoline engines, so trying to put both on the same car would incur a double price premium and not enough people would want to pay it.

[–] Death_Equity@lemmy.world 3 points 2 days ago

It's just a diesel range extender, they wouldn't have to use all that big of an engine. Just like on locomotives, the diesel is just is a generator to power electric motors. No integration into the drive line, the diesel has a generator on it that feeds the batteries.

One guy put a diesel engine in a Tesla as a range extender and it had a range of over 2,500 miles. It got like a 400mpg.