My uncle who restores old Ih Farmalls told me that, he never rebuilds the engine due to that esact thing. It has something to do with teh sleeves having to be heat treated for everythgin to seat properly. One thing different about car engines versus tractor engines is there are sleevees in tractors and they run at lower but steady rpms and are a "lugging" type engine.
Plus how many car engines will have the hours on them that some of these tractors get, and remember that the tractor engines for the most past are at peak operating engine speed whereas a car fluctuates, idles, and rarely ever sees it's peak HP rpm range.