It's to prevent police corruption.

Let's say in country A, they think a certain kind of medicine is bad for everyone, so it's illegal. But in country B, they think it's safe, so it's allowed. Police from country A can't just go to country B and start arresting everyone who uses it. That's not following the law of the land.

[Mind these are completely different matters but look if it gets the baby to be quiet it's worth a shot.]