I don't really understand why the weights aren't included... US law says they can't have a copyright, no? Maybe they're concerned about other countries or cautious about a litigious Nvidia.
There is an argument that it's a derivative work and it's therefore copyrighted under the same protection as the training data, but that gives the rights to the owners of the training data, not the ai-lab. Courts are seemingly mostly rejecting this though as it's different enough to be fair use.