Why wouldn't being banned from serving as CEO or Chairman of any publicly traded company for some certain amount of time be enough? Why wouldn't increasing the fine be enough? Say it were $40m, $80m, $100m.

You can punish someone without throwing them into a box. I don't see how that benefits Musk or society in any way. If he's unlikely to do anything like this again, he had power taken away from him, and investors recooped losses, what possible gain is there?