The power requirements of a farm tractor are much more suitable to a diesel than a spark ignition; constant speed heavy work load. I’ve got an old Minneapolis-Moline 445 gasoline tractor that runs on either gasoline or ethanol. It gets much better low end torque than my newer diesel tractor, but it just sucks down fuel by comparison.
Yep - both of my plows run on gas, because a diesel would eat the transmission in one season.
Sure, they suck fuel - but when somebody is paying $250/hr to move them, who cares?
Check out the compression ratio on those old gas engines. They’re low - real low. Like 6.5 to about 8:1 or so.
High Carnot efficiency, they’ll never have. ;-)