It comes from those that really short trip their vehicles. It is very hard on the oil if it is only driven 2-3 miles, shut down for 6-8 hours, then driven 2-3 miles home, day after day.
You may only have 1500 miles on the oil in a year, but very hard miles.
Then you may have someone that drives their vehicle once a month, but drives it 100 miles on the highway. 1200 miles in a year, but the oil is just fine.
Auto manufacturers have to dumb it down to the lowest factor, so they just say xxxx miles or once a year.
My mom's Kia says 6 months max, which is a waste of oil. She drives maybe 2,000 miles in 6 months, with varied driving.
I save the oil from her vehicle for top off oil for my truck that has not had a change in 18 months (~3200 miles, uses a qt of oil every 1000 miles or so) and not sure when I will change it.