@cicerone imposter,
It's been explained to you ci. on a number of occasions. There are a number of reasons but they all boil down to the same thing. It's economic.
But I have accepted now that you will not dispute any of the arguments and enjoy asking you silly question because it gives you a sense of being wise, tolerant and clever.
All it proves if New York acquiesces to the demands being made is that it has acquisesced. Presumably marriage to a sister or mother comes next. Or sister's half sister. Or mother's sister. Or mother's daughter by another man.
It's associated with exogamy and making people look for new blood. If a sex can be endogamous, officially, as homosexuals seek to be, despite being now allowed to be unofficially, except in the small states mentioned, seafaring traditions being still strong there, except Iowa, for reasons I couldn't begin to speculate upon, then the door is open to arguments along exactly the same lines you are using in this case, for family endogamy which, of course, inhibits geographical exogamy. Slowly enough at first for you not to think it is of any importance but then you never do think anything is of any importance if it stands against what you want.
Members of families love each other more often than not. Although what love means has not been decided yet. Or can ever be truly validated. But with declarations being considered validations in your neck of the woods, Stupidville, I don't suppose you will understand what I'm talking about. And perhaps that is for the best.