In our case health, family and home remodel issues intervened in our plans for active motorhoming. As a result our 2004 rig has very low miles on the odo but has had roof AC, fridge, converter, batteries etc., replaced at about 10 year point.
I wouldn't be surprised that others have had similar issues especially with older couple owners. I suspect that job losses and career setbacks are also behind curtailed RV usage. This could be an advantage for cautious buyers. Motorhomers are said to average about 5K miles per year.