Except that every able bodied man was assumed to be a member of the militia. This is because the idiots who wrote the 2nd amendment didn't want a standing army.
Then the war of 1812 happened and everyone was like "oh shit, maybe there was a reason why standing armies exist" and then the 2nd amendment was forgotten for a century. A bad idea that didn't work out.
It's kind of like the 3rd amendment. Important at the time, but actually meaningless in practice.