You're suggesting they tell owners "change the oil every 10k miles" so that the engines will die of oil-related failures after 60k miles or soon after ? And if that were to happen, people will run out and buy another model from the company ?Sure, but do they have a vested interest in engines that last several times the warranty period
Don't get me wrong, if someone wants to change synthetic oil every 3000 miles, more power to 'em ! This site, other sites, oil analysis results, and so on have shown that engines aren't dying from using manufacturer-suggested oil change intervals.