I think this is because Bitcoin promotes anonymity, buying marijuana using Bitcoin maybe dangerous since it doesnt required so much things amd possibly this will lead for them to buy excessive one and probably will cause over dosing pr addiction. As far as I know Canada is also dtrict with allowing marijuana , and it js encourage only for the sake of medical purposes.
No, the article state about protection of personal information, buying bitcoin could help as in terms of transaction it's more transparent but anyone can hide their real information and there will be no trail of transaction that would lead to their real identity.
Bitcoin is very useful on this type of transaction, it would help the government if they will study to implement this.