Yeah, does seem like a pretty screwy idea now or then. I believe it was born out of a Depression-era mindset where the struggling farm family would not have to buy a car/truck AND tractor when they could just buy one of MM's ComforTractors and have both.
Well, it was still pretty much tractor (no power steering, iffy tractor breaks of the time, no suspension, bad visibility for either a car or tractor) and not car and didn't go anywhere.
We find it funny to think of car-like amenities and high speed road gears on a tractor, but in Europe today they use their tractors very often on highways as prime movers much, much more so than we would ever consider doing in N.A. Items such as the highway tranny, suspension, modern brakes, etc are all in place on many Euro-spec machines today to achieve better highway handling.