"People" in this instance is a handful of special edge cases compared to the majority of computer users, even if we're only looking at people that build their own computer, or hell, even just looking at only linux users. Dual booting is a minority. Yes, you CAN do it. Linux has made it easy. Great! But not many DO.

Nobody gives hell to every other OS manufacturer that will clobber our current bootloader configs. That means more than OSX, btw.