[devonin]

It was made illegal when nobody in official power knew much of anything about it, and so far, nobody has been willing to admit that they were reactionary and acted before they had proper knowledge of what it was and how it worked (Go watch 'Reefer Madness') so it remains illegal.

Prohibition is the only amendment they've -ever- repealed and making -anything- legal -after- you already explicitly made it illegal happens incredibly rarely and generally takes exceptionally large popular demand for the change.