I'm guessing here, but it seems most states that recognize "trikes" as a motorcycle with no more than 3 wheels touching the ground at any one time allow the out rigger type trikes because on a level surface only 3 of those 4 would touch the ground. To be fair, the criteria would need to be consistent. So that would probably mean full fluids (brake, fuel, engine lubrication & coolant) without anybody sitting on it since rider weight can vary widely.
That would mean the bike would lean ever so slightly to one side or another. Tip it the other way and at one point there may only be the front and rear tire touching before leaning far enough the other way for the outrigger wheel on that side to touch down. All 4 might end up touching the ground most of the time once the bike is loaded with a rider at least; and more so with a passenger & gear. And road surfaces may vary from time to time so there would be no way to reasonably expect that all 4 tires would not touch the ground at the same time at some time while riding..
This all may not be entirely true or correct, but is just what makes sense to me.
Southeast Michigan Dark Side Rider 4 Honda Reflex scooters & a Big Ruckus Originator of the "Darkside" Honda Reflex. "Yeah dude, that IS a car tire there on the back of my scooter." Sometimes I'm so far outside of the box, the Hubble telescope can't find me
The old Lambretta's 3 wheeled trucks with the 300 something cc engines had a 4 ton (8,000 lb) load capacity and would probably be a good starting point. They even had a refrigerator delivery truck version which may not even require a new thermostat to set it at say 75 degrees.