[Z]

There are benefits of forging relations with your default allies though. Combined, the UK and South Korea could force some counter leverage on the US in the event of any kind of conflict of interests, e.g. when the UK voted against going into Syria and relations became frosty between the US and UK. If the UK had better relations with some of the US's other allies, they could only potentially benefit, there would be no drawbacks and the US wouldn't be able to do anything about it. It's a bit like how Russia has control over all of the Central Asian -stan countries and some Eastern European countries yet none of them have real relations with each other; it's all down to Russia.