The reason is quite simple, and it comes from the Hon. John A. Gibney, Jr. United States District Judge for the Eastern District for Virginia, writing in his decision in Tisdale v. Obama:
It is well settled that those born in the United States are considered natural born citizens.
I like to cite a long list of court decisions on the issue of Obama’s eligibility to refute the claims that US Presidents must always have citizen parents. I use the list because it’s impressive, but there’s something more important than its length, and that is its uniformity. Judge Gibney says that the question is well settled, and that list of cases demonstrates that it is settled. All the courts that have ruled on the merits in all the states where Obama’s eligibility has been challenged on the basis of his father’s status have gone the same way.
The Supreme Court gets involved when there are differences between the circuits, or between state supreme courts or between federal and state courts. There are no differences on this issue; it’s settled. The US Supreme Court will not review it. That was a rough summary of Supreme Court Rule 10. Considerations Governing Review on Writ of Certiorari. There is one additional situation where the Supreme Court might review a decision:
(c) a state court or a United States court of appeals has decided an important question of federal law that has not been, but should be, settled by this Court, or has decided an important federal question in a way that conflicts with relevant decisions of this Court.
I suppose this where the birthers must hang their hopes; however, the essential issues were already decided by SCOTUS in 1898 in the case of US v. Wong and nothing in the more recent decisions conflicts with that. Birthers will say, of course, that the state decisions and the one federal decision are contrary to the Supreme Court’s decision in Minor v. Happersett, but that’s just because they don’t understand that case.
One might argue that the Supreme Court can hear any case it wants to. That’s true, but there have been several birther cases already that it could have heard if it wanted to weigh in on the issue. It didn’t.