Exactly right. You're able to privately resell contract keys (and the buyer can then re-issue a new key with their delivery info, voiding the old one), but onionfutures.com doesn't facilitate it.
The specific laws do not actually ban the transfer of those contracts (tbf this is very complex and depends on your reading). And yes they do not facilitate the trading of the instruments in the secondary market but they absolutely facilitate the instruments themselves otherwise there cannot be a secondary market without any backers of the instruments.