Why don't tractors have seat belts?

Some do. There are different tractors for different purposes. Also has to do with the size of the land a tractor is supposed to cover. Some are VERY comfortable because you may sit there for 5 - 8 hours. Air conditioning, a stereo, air suspended seat. Those have seat belts. Smaller tractors more for one man operations do NOT. The reason I would say is because you are on and off the machine so often, may have a reason to shut it off, jump off and fix something that mucked up the works. Also as YOU observe, the terrain may be rough, uneven ground. You may want to bail off the high side if the tractor rolls over. A Tractor IS a dangerous machine if you are NOT very careful what you are doing. That PTO (power take off that runs the implement being pulled) has grabbed many a Farmer.

Maybe they do these days. Seems smart.

Quote "You'd think they would be more necessary than even on cars because of how dangerous the machinery" ...no i wouldn't that's your thoughts not mine, seat belts are included in most vechiles because of thier potential speed,, and the damage that could cause in an impact situation...it actually imho makes no sense in a tractor imho it would be an extra danger in such a vechile in most scenarios,   you may want/need to get clear of the vechile and a seat belt slows down this process,   and you really shouldn't be having high speed impacts in one, given there speed and amount of time to see a potential collision happening..

Better still, why not ejector seats? 🤾🏽‍♂️

I guess farmers pay attention to what they're doing while they operate heavy equipment