True, but that's not to say that they couldn't. Its just that demand hasn't dictated that manufacturers build one.
I've seen 6500-lb diesel trucks pull mid-11 second runs on less displacement than a C6 and still get 20/26 mpg. And they can tow 12,000 lbs
The bottom line is that diesel fuel contains more BTUs than gasoline, less of it gets absorbed by the coolant, and the higher compression is potentially capable of converting more of those stored BTUs into work. The fact that they don't is as much from stunted development in the market as it is from the heavy components the used to go into the engines themselves.
Some of the most incredible output comes from the larger industrial/agricultural diesels where the market sees its value. The technology that has trickled into the automotive market largely came from agricultural diesel advancements, but until the automotive market truly embraces diesel, it won't be profitable to bring it down from the tractors. I wish it were the other way around, but it doesn't seem to be going that way.