I think they assume you are maybe doing shorter trips, which can be more detrimental to the lubricants. Some newer cars however take this into consideration, and use a sophisticated algorithm to determine when service is required.
My Sprinter, which does NOT have the flexible interval minder (ASSYST), and just has a fixed 20,000 mile or 24 month, recently had its service reminder come on. I do not even have 10k miles on it quite yet, but it is 24 months out of the factory. Since 95% of its driven miles have been cruising down the highway, I am not all that concerned about the time. But the onboard system in mine does not keep track of that sort of thing. The ASSYST equipped ones do. Similar to many GM vehicles.
We have some GM fleet vehicles that do lots of highway driving, piled on pretty quickly, that will come in here for service at 5k miles (because that is what the dumbass fleet management people want
) and they will still show 65% remaining oil service life, and on the non-turbo portinjected ones, the oil will generally still look fine and still be within the operational range. Of course, that crappy little 1.4L turbo they have will be 2 quarts low and full of black burnt tar water after 5k miles.
But in the end, they are probably just wanting to be sure the hood actually gets opened (where applicable) and the oil gets checked. You'd be surprised how many people cannot do that. I check the oil of every car that comes through our door (save for the few EVs) and you'd be shocked how many are low. EVERY Subaru that comes in here is low... no matter if they are due for service or not. And we service a fleet of those turds that are all 2015+, and they cannot go more than about 2500 miles before the oil level is below the operational range on the dipstick. They've already blown up a few.
FWIW, I have quite a few cars, and I still go by miles no matter what. The only exception will be the Sprinter, as I will change its factory fill at 10k miles instead of 20k, which will have it likely around 27 months from its build date. If I were driving it more I'd go the full 20k. I change my F150's oil every 5k miles, which can be about once every year or so, as I do not drive it all that much.
I would say just keep an eye on the oil level and use your best judgement. If you rarely drive a car, but when you do it is just a short trip, you may want to change it more frequently. We are seeing more of an oil dilution problem with DI gassers like we did back with carburetted engines, especially in cold weather and short trips.