As a Portuguese who was alive (albeit a kid) in the 90s, I can summarize this as we didn't have enough resources (both human and monetary) to keep enforcing the U.S. drug war model. Since it wasn't working and we were reaching a critical situation (like half of Lisbon in particular was filled with drug addicts shooting heroin up their veins), we turned to the experts.
The article implies this was a decision made from the beginning of this epidemic, but it was pretty much a last resort because the other model was unsustainable for the government. Not sure if we would've adopted it if we had US' resources.
Also, just giving context here, not trying to diminish this accomplishment.