You might be too young to remember 30 years ago but believe me, 3000 mile drain intervals were not the accepted drain interval in 1973. 1500-2000 mile intervals were alot more common until the late 70's to early 80's.
I believe the quick lubes had alot to do with it and marketing.
What puzzles me is that more people don't go with a 5000 mile interval, since it's easier to remember on your odometer.
In Canada, the 3k oil change is easier for most people to remember simply because our odometers are in kilometers, and 3k is roughly 5000km. Although I still think a lot of people up here should just be going with a 10,000km interval (6200mi) for simplicity.