I don't understand all the legalize, but why would he have had to do this? Didn't the congress file it with the courts asking to do a de novo?
Because the courts aren't supposed to reach beyond the evidence presented to them. The burden, once that law was passed, was squarely on Gibbs. We get snarky when Justice Kennedy starts citing foreign law. In this case, the courts stayed within the boundaries of the law, and now we're PO'd at them because they didn't take an activist posture.
Didn't the congress file it with the courts asking to do a de novo?
Congress filed no case. They merely passed a law.