Another reason no challenge appeared might have been the sunset provision in the AWB. Short of a re-authorization by Congress, in 2004, it would go away.
Considering the previously mentioned difficulties a State would have bringing a case (proving harm to the state), plus the time, and the cost (also applying to an individual or class action case),combined with the sunset provision made it really a pointless endeavor, outside of the principle involved.
Why spend years and likely hundreds of thousands of dollars (all inclusive) and either a) fail -get the case tossed on a technicality, or simply refused to be heard by the High Court, or b) win the case, 8 months before the law expires anyway? (ok, 8mo is just a random choice, but you get the idea)
All else being equal (and it almost never is) bigger bullets tend to work better.