The answer is "tradition" which is another way of saying (in politics): "Nobody knows, we've just always done it this way, and we can't conceive of changing it."

In truth, though, IA and NH haven't "always gone first." NH began doing so back in the 1950s, and IA in 1972. So it's not even that old a tradition.

And you're right, any other state could pass a "me first" law, but NH has already thought of that. Much like a kid saying "...until infinity" to win an argument, or using one of the genie's three wishes to wish for more wishes, NH's law states "our primary will be held two weeks before any other primary." If other states move their dates up, it's automatic (built into the law) that NH moves theirs two weeks before it.

IA is different because it's a caucus, not a primary, so it happens even before NH. But Republicans have held caucuses in Alaska and Hawaii before IA, so what you have described has already happened on the GOP side. Why nobody mentions this I'm not sure, possibly because the contiguous 48 states routinely ignored AK and HI (unless they're building bridges to nowhere).

Thanks for commenting.

-CW