Well, if for decades oil has been changed after every 5k, 6k or 10k miles, it's hard to change that. It becomes little like a religion, even if such a frequent change is not necessary with modern engines and full synthetic oils, most still believe the old ways.
I'm quite sure there is no need to change oil in US or Canada after every 5k or even 10k miles. Here in EU, longer 12k (20k km) and even more commonly 18k mile (30k km) service intervals have been used for years. You wouldn't sell a single car here with 5k or 6k mile service interval.
But on the other side, you wouldn't sell a single car in US with 18k service interval. I mean Volvo could just change the interval from 10k miles or whatever it is to 18k and I'm quite sure technically nothing would happen with the engines. They would run like before, for years. But it's a question of belief. If for decades it has been told, that oil must be changed every 5k miles and now someone says it's 18k miles, it's hard to believe.