>Tires shocks and brakes all of these other things are usually repaired within a certain cycle of mileage, but the major indicator trying to figure out if a 50,000 mi which car versus 150,000 mileage car, could be incredibly different if I lived in a very urban area and perhaps sat in my car with the engine running for several hours. I'm just confused why this never was taken into account but it seems like from one of the answers that this is kind of just been the de facto standard and hasn't really ever been updated.

Highway miles are easier but only a little and it still depends on soo much. A car with 60k miles driven on a nice highway may be in better condition than one with 50k driven in the city but one with 50k driven on crappy bumpy highways may be in worse shape than the one with 60k city miles in a place with nice roads and no salt. A car with 100k highway miles is still wayyy closer to the end of its life than one with 50k miles of any variety

Each bump, vibration, start, and stop stresses various systems. Highway speeds are easier on the engine and transmission because they're staying in their happy zone but higher speed bumps are harsher on the body and suspension.

The mileage is just a guideline as higher mile cars are in general closer to the end of their life, but you really can't capture all the little differences which is why there's also a quality grade for the condition of the vehicle and you should get it checked out.

You fundamentally cannot make a perfectly accurate pricing tool for cars, there are wayyy too many variables for someone to punch in which is why you generally get a price range and there's a qualitative assessment after that.