Let's say you're Iceland. When international laws are created, e.g. making it illegal to poach an animal close to falling on the endangered species list, you feel much pressure to obey it. Even if the hunting of this animal is a sizable industry for your country, other countries can respond by imposing trade sanctions on you, etc. to the point where it simply isn't worth it to fight them.
But, if you're bigger than the country who could impose the sanction on you, they would be afraid to do anything in fear of any economic retaliation.
Yes, you know what I'm hinting at. It's time to take Canada.