I cannot speak to Jeeps.
Tractors are produced in minuscule unit volume relative to highway vehicles but with a great number of individual models relative to unit volume.
This model disbursion has been the case since the late 1950's, when Harry Ferguson's patents on the Three Point Hitch expired and the TPH became public domain.
If you have an old tractor that was sold in volume parts are probably still available. If you have an old tractor that was dropped after only a few thousand were produced, parts are probably not available. (Deere is a partial exception to this, as Deere has a dedicated plant in Waterloo, Iowa, which fabricates parts for what are termed Deere "legacy" models. As logic would indicate, legacy parts produced in short production runs are very expensive.)
So parts availability affects resale.
As do tractor improvements since Ferguson licensed his TPH to Henry Ford in 1939. In approximate order: 4-WD, Power Steering, Industrial Tires, Loaders, Diesel Engines, Landscaping tractors <2,000 pounds bare tractor weight, Cabs with heat and AC, "independent" PTO. And, continuously, shielding separating operator from revolving parts.
I have operated several generations of Deere tractors for neighbors, a few days on each. I hugely prefer my Kubota Grand L. This is not to disparage Deere, it is a comment on continuous minor improvements in tractors across surviving tractor brands.
DEFUNCT TRACTOR BRANDS:
https://www.tractorbynet.com/forums...-tractor-manufacturers.html?highlight=defunct