I presume the main reason for the controversy is the prevailing dogma "Drugs are evil".
This dogma has been used to enact countless bills of legislation in most rich countries, which in turn have encumbered the justice and police system, which in turn have put thousands upon thousands of people into to the
correctional system for years.
After all that busywork, lives destroyed and taxpayer money wasted, it is really hard to suddenly jump ship and say "Nah, you know what... after all these lives destroyed and billions of tax money spent ... you know, we were wrong, let's rethink this".
Drug abuse should be handled as a public health issue, not a criminal issue. And it takes time and effort to rebalance the current status quo to a more humane and sane approach.
This vox article discsusses the political history of war on drugs:
https://www.vox.com/2016/3/29/11325750/nixon-war-on-drugs