Well, it is not apparently self evident to Chief Justice Roberts and Justices Scalia, Thomas and Alito who have not voted to accept any case involving the NBC question.
Yes, it’s obvious what natural born citizen means.
Since SCOTUS hasn’t said why they denied anything, let alone ‘denied because we think Obama is a natural born citizen’, it could mean any number of things. Bad presentation by the lawyer, timing, standing, wrong person sued, incorrect precedence cited, etc.. Maybe they don’t want to risk riots just yet, and will give it a few months or a year. Maybe they’re scared. Maybe they think it’s not their place.
I have no idea, but probably last on that list is them not knowing about the Constitution...
However, if there are 5 of 9 that are ‘living Constitutionalists’, for example, and voted to change it to shoe-horn in Obama, they’d be making a huge mistake. I suspect there is much more going on here with the attack on the Constitution and on U.S. sovereignty, but so far, SCOTUS isn’t talking.