You mentioned about mileage. RV mileage is a little different than car mileage. The biggest killer to RVs is that they tend to sit unused for extended periods of time. Low mileage for the year can mean the rig sat unused for a very long time. When an RV sits, condensation builds up and it never get aired out. This can tend to make wiring corrode. It also dries up the seals inside the engine and trans. The inside of the engine can rust.
Think about the guy who sold that coach to a used car dealer. Anyone who would trade their coach to buy a used car, quit using the coach long before they traded it. Someone who trades to an RV dealer would likely have used the coach and was upgrading. The odds are very high that coach has sat unused.