I've let people I know well and trust borrow my truck; but I'd never let them borrow my tractor. Regular cars and trucks, most people know how to properly use them.
A tractor is a specialized piece of equipment and in the hands of an inexperienced person, can be deadly.
It takes hundreds of hours of use to become proficient at safely operating a tractor with a loader, backhoe, or powered attachments.
You want to "borrow" my tractor, I come with it as the operator. Same thing goes if I have a job too big for my tractor. I'll ask a friend with an excavator or dozer to come over to do the job either for pay or trade; I'd never ask to borrow it without him. And if I absolutely have to do the job myself, I'll rent one before I risk his.
I've found the concept isn't unique to tractor owners. I took up fencing in the past couple years (with swords, not barbed wire.) Proper etiquette for borrowing another person's sword is that if you break it or damage it, you replace it or fix it with the same value or better, no questions asked. The one thing I have noticed in several posts in this thread where a borrower broke the tractor; none of them repaired it, offered to repair it, and in some cases didn't even mention they broke it. Fortunately, no one has mentioned loaning out their tractor to some one and they got hurt or killed using it. But I imagine it has happened, and probably too frequently.