They initially were in it, but I have the impression they wanted to combine it with another case somehow because of the composition of SCOTUS at the time that it first went to the district court. They were afraid of losing, which is not unreasonable with some of SCOTUS' recent 5 - 4 rulings with the left winning.
They had a falling out with the lawyers of Parker et al. because of that. The NRA did file an amicus brief for this appeal to the Circuit Court. See page two of the decision.
Any corrections will be appreciated.
Have you thought about that? They were afraid of losing a case involving the 2nd amendment? Oh well, the fearless Cato Institute has one upped them.
The guy behind Parker knew he had a good case, and was funding & running it himself, and didn't want anyone else screwing it up.
In the end, Seegars failed, and Parker very nearly did (only plaintiff Heller maintained standing thru the latest verdict).