Because in this country we prefer to declare on things we don't like instead of actually addressing them correctly.

Prohibition taught us this, people will do what they're going to do, you're either going to make them a criminal for it and spark a black market making things way worse or you're going to be responsible and develop a system that allows them the freedom to engage in that behavior in a safe and regulated way with reasonable punishments for breaking those rules.

In my insane opinion, all drugs should be legal and regulated so we can kill the black markets, but realistically I understand that some of those, like meth or fentanyl, are pretty much just addictive poison and will likely never be fully legalized the way alcohol was again after prohibition and weed is being legalized again right now.