Why is the 1933 Double Eagle illegal?

Could you please explain why the 1933 Double Eagle coin is considered illegal? I'm curious about the historical context behind this and how it came to be prohibited. Was there a specific event or policy that led to its outlawing? Additionally, I'm interested in knowing if there are any exceptions to this rule or if there have been any attempts to legalize its ownership and trade in recent years. Lastly, what are the consequences for those who possess or attempt to sell this coin illegally?