Agreed, but if you don't address the demand problem you can't beat the supply problem. And that's where we are now.
Plus, as long as drug trade remains illegal, you have secondary problems such as bribery of officials, gang violence.
AFAIK, we do not have anything like asset seizure in Germany. And the prison system over here is much less privatized / industrialized, so is not exactly a profit center.
A well-staffed, well-trained law enforcement apparatus is fairly expensive, too.
And consider that without proper treatment, widespread drug use incurs costs that do not show up on government budgets as such. Drug-related crime (theft, burglaries, etc.) comes to mind.