Keep in mind the smaller motors don't have to comply to the regulations that a larger motor does. That is also why if you notice the lawnmowers now are set to run at one speed. You start it and it is running full speed and there are no throttle controls.
A gas tractor could work and would work except for a few things.
1. Most all large equipment is setup for diesel so for things like tractors there is probably already a good fuel supply and depending on the work site they might only have diesel.
2. Gas equipment is thirsty. Plow with the Oliver 770, would start out in the morning with a full 20 gallon tank, come in for lunch and have to fill it, go out in the afternoon and come back at night and have to fill it again. The gas tractors always had to get refilled more often. Working the tractors hard, the gas tractors would never last the day without a fill up.
That being said some things have changed.
1. Gas engines last so much longer than they used to, the life expectancy gap has narrowed.
2. Emissions items on gas motors are well known and proven.
3. Gas engines will start when it is horrifically cold. Though modern diesels have closed this gap a lot as well.
On a side note. That horrible ethanol fuel runs just fine in the 1952 Oliver 77 (still used a lot), 1951 IH Super C, 1958 Chevy ton and a half truck, 64 Chevy 1 ton, 1967 Oliver 770 (still used a lot), 69 Road Runner, 70 Nova SS, 74 Dodge powerwagon, 75 dodge W200, 91 GMC Sonoma and other vehicles. It runs fine in my lawnmowers, chainsaws and trimmers since the mid 80s just fine. Oh and I never run them dry, I store wet filled to the top. I can grab my chainsaw after sitting 8 months, give it choke and fire it up without any issues. I fired up my 74 powerwagon after almost a year of sitting with E10 in the tank and it ran great.
I know there might be some issues but I think 95% of the time people blame E10 for motor issues because the mechanic sucks or they don't want to tell the engine owner he doesn't know how to take care of his stuff.