Earlier quoted context omitted.
They used to have UK legal presence, and planning to move out. The UK is saying something like "crimes done during your presence won't be ignored". If Imgur never had UK presence, then yeah there would be no teeth. But if you're doing business in a country you can't break the law then leave and expect them to just ignore what you did during that time.
…but how enforceable would the fine be? They pull out and have no UK assets to seize.
American companies are too use to being able to bully their way in America. Some countries do have better consumer protection laws.