In reality obtaining diesel is like separating cream from raw milk. Its always there. It isn’t a matter of an inefficient process to make Diesel vs. gasoline. Diesel is one of the easiest parts of Crude to retrieve and until the past couple of decades there was little more to do than to boil the oil, add a touch of chemicals, and clean it up a bit to get it. (Gov regulations require the refiners to remove more sulfur which is a costly process now.)

In fact to extract more gasoline, Crude runs through a plethora of additional (and costly) processes in order to increase the amount/fraction of recovered gasoline. Sometimes the oils for diesel are converted to lighter products that are added to gasoline in processes that modify the molecules. I.e. the Refiners sometimes forcefully reduce the naturally occuring diesel parts into gasoline parts. So, diesel generally takes less energy and cost to obtain. (This doesn’t mean though that the use of diesel is better or worse for the environment.)

A side note is that Natural Gas may become a low cost and cleaner alternative for diesel (and gasoline?). There are industries that are working on mainstreaming this as an alternative fuel for diesel trucks (and some cars?). The technology exists and is in use. They are just working to mainstream it. Currently Natural Gas is at a very serious low in the market price making it very attractive on a straight economic basis. The real challenge is to create an entire industry to make/convert/support such vehicles on a large scale.

Yes, my 1995 Honda.

My 1966 Dodge Dart got 22 mpg. I laugh when I see car and truck manufacturers bragging about 22 mpg. Heck, the 1908 Model T got 18 mpg!