Iowa (Iowa for pete's sake!) already ruled that state law prohibiting same sex unions/marriage was invalid:

"Iowa lawmakers have "excluded a historically disfavored class of persons from a supremely important civil institution without a constitutionally sufficient justification."

To issue any other decision, the justices said, "would be an abdication of our constitutional duty.""

California's Prop 8 ( 8 = hate ) was upheld because the complaint against it said it illegally amended the state constitution.

I think they were avoiding testing deeper waters to see if they could get it repealed this way.

States rights seem to fly based on the administration in charge at the federal level.