I don't know the exact law, but I believe it has to do with licensing rights. You're bypassing a business license by viewing content via a service that is not licensed to broadcast said content in your country. I think it's technically a gray area still, but there's probably a legal precedent for it, I just don't know it offhand. I think it's a horrible anti-consumer business practice that needs to be reformed, but if you're not going to pay for the legitimate way to consume the content, I'd say using a VPN to watch it where it's legal in another country, I'd say that's the lesser of two evils. At least they're still making some profit from your viewership.