Some people don't drive that much. Even better if they live close to work and don't have to drive so much. Having another car IMO is a waste unless it's a free company vehicle and even then it hadn't better be a coffin on wheels econobox. IMO low miles is flat irreverent as most 5.9's have stupid high miles on them and anything under or even close to and slightly over 100K on the clock is a rare gem. When I was looking for a 5.9 I could find any high priced truck I wanted with 200 - 500 K on it. Searching under 100K things get expensive/rare quick. Better said to hold their value. Only applies to 4x4, crew cab, and the rest be small 'options'. No CC or 4x4 and the value is way less, but still rare. 4X4 or Crew Cab = 10K price difference.
Being on both sides of the high/low mile coin: reasons do vary for owning a diesel truck. Hauling the only RV once a year or 100K put on in a year. Even DD as they don't make a station wagon anymore... I won't be caught dead in a 40MPG econo box because of an Elk encounter. :-laf Already been caught in a totaled 3/4 ton truck with a flattened elk as it is.
So you are really asking about the rare low mile trucks - made even rarer as people who paid a lot for them hang on to them. After all the 5.9 is irreplaceable as the new stuff has lower MPG, less reliability, plastic bumpers, and higher maintenance with emissions. Regardless this is the USA and everything is for sale for the right price.