Why shouldn’t that be required?
Because it's not spelled out in the Constitution.
And because it's ultimately up to the voters to decide. After all, Billy Ayers fits the Constitution to a tee. But should he be President? The Constitution says OK. Any normal person says "Hell, No!".
Expecting the Constitution to fix stupid fails. We saw that in 2008 and 2012. Let's make sure it doesn't happen in 2016!
Neither is the term "Letters of Marque", but apparently the Founders knew what that term meant.