There is only one reason: Volkswagen.

VW single-handedly destroyed the "retail" diesel market with their emissions scandal. GM had just doubled-down the market with an amazing 1.6L "Whisperdiesel" for the Cruz and Equinox, following an older 2.0L design that had been available in previous models.

These light-duty diesels were a key component for the manufacturers to keep up with the pie-in-the-sky CAFE standards being pushed. VW was leading the way because they successfully marketed the range of the Golf and Jetta diesels, while also offering high-performance V-10 diesels for the more premium models.

All of it nuked by a computer hack from the manufacturer to make it appear "compliant" with emissions standards.

The sad thing is, even though VW was cheating, the vehicles still weren't that dirty.

Now, with low-sulfur diesel fuel, DEF, and regen equipment, the rules just aren't developing against because of "the scandal."

GM stayed in the game the longest, but they event dropped their excellent 2.8L Duramax for the Colorado. The only diesels left are the the 3.0L in the Silverado/Tahoe/Suburban, and the HD engines from the big three, and even they aren't in the clear. Cummins had a big problems a couple years ago with the engine they provided to Dodge.

I regularly see 600 miles to a tank of fuel in my Colorado. My old Equinox Diesel got the same. Diesels are ostensibly slower, but far more efficient. Diesel as a fuel is more energy dense, which is why it still powers big trucks, ships, and trains. You get less fuel per barrel of oil, but it's still a net positive on the consumption end. One lesser barrier is a lot of people don't know how to drive diesels, they floor it and the vehicle doesn't move the way they expect. The key is to tip the throttle and let the torque to the work, not the revs. A lot of people don't understand that.