Easy answer. Because the law says so. And not some "** BATF law." BATF does not make laws (although they do make regulations). That law is clear and it was passed by OUR representatives in Congress and signed by OUR president. If WE continue to vote for these guys, or continue to sit back and not vote, we get what we deserve.
Bob 89 - You may not be able to buy mail order ammo, but if you are old enough to vote and don't, I don't want to listen to your gripes.