I don’t think it’s much besides people becoming more lax on maintenance as the car ages.
Most people are going to adhere to the oil change schedule no matter what. But if the schedule is calling for new spark plugs every 60,000 miles it will almost certainly happen at 60,000 miles but maybe not at 120,000. Instead people will probably wait until something is going wrong enough that a mechanic tells them they have to replace them.
Or things that don’t last forever but don’t have a set replacement schedule. The oxygen sensor, PCV valve, etc. I just replaced the PCV valve for the very first time on a Subaru with 130k miles on it and the mpg jumped by 2-3 immediately.
Most people are going to adhere to the oil change schedule no matter what. But if the schedule is calling for new spark plugs every 60,000 miles it will almost certainly happen at 60,000 miles but maybe not at 120,000. Instead people will probably wait until something is going wrong enough that a mechanic tells them they have to replace them.
Or things that don’t last forever but don’t have a set replacement schedule. The oxygen sensor, PCV valve, etc. I just replaced the PCV valve for the very first time on a Subaru with 130k miles on it and the mpg jumped by 2-3 immediately.