More that they know enough about how it works that they know it's impossible to do. The data isn't stored like files on a hard drive, in some discrete bundle of bytes somewhere, and the problem is simply trying to find and erase them. It's stored as a distributed haze of weightings spread out over all of the nodes in the network, blended with all the other distributed hazes of everything else that the AI knows. A court may as well order a human to forget a specific fact, memories are stored in a similar manner.

Best the law can probably do right now is forbid AIs from speaking about certain facts. And even then as we've seen with the like of ChatGPT there will be ways to talk around such bans.