It just wasn't done, but was it actually illegal? Certainly I expect that more than a few states had antimiscigenation laws, but was that written into the civil marriage act?
As proof of how quickly our country (or some parts of it) advances, know that
South Carolina had a ban on interracial marriages until 1998 and Alabama didn't remove their law until late 2000.
Its even more interesting to read that nearly 40% of the votes in AL that were cast on the issue were for keeping the law on the books.