In this case I think the times have changed but old advice has stuck. From my understanding, cars until the 80s or so did need their oil changed this often, but newer cars with EFI and especially if you use synthetic, its no longer necessary to do so. Its been many years since I bought a new car, but IIRC even the mid 2000s you were supposed to get an oil change relatively soon after getting a car as fine particles that weren't entirely machined off should have been worked off in the first thousand miles or so and you were told to get an oil change then.

There is also the case of changing oil for hot and cold seasons- getting thinner oil in the winter and thicker in warmer weather to adjust. I think thats more or less a thing of the past as well, my Honda does not specify/recommend this in the owners manual but perhaps some cars do?

Old adages sometimes stick around forever though- especially when there is money to be made in keeping them alive.