The US has a variety of justifications for having hundreds of thousands of troops and thousands of bases overseas. The US presence in Japan and South Korea, in particular, is contingent on the North Korean threat. If North Korea ceases to be a threat, the US troops stationed in South Korea and Japan will have even less support from local populations then they have now.
This is why the US politicians and the mainstream media cheerleaders continue to cast DPRK as an extreme threat.
Or, alternatively, the US would need to cast China into the villain role that DPRK currently fills. Unfortunately, there is so much Won, Yen, and USD invested in China that making China into the next pariah would be deeply unpopular with the powerful investment classes in these countries.
Most of the other countries you mention in the question - UK Commonwealth, France, etc - no longer have a large overseas presence due to the end of colonialism. Therefore, they have no interest in having a large troop presence in East Asia. Said another way, these countries now trust the US to "police the world" and enforce post-colonial international security.
Sooo... the US, the most powerful nation in the world, uses DPRK as a justification to station troops and nuclear weapon in its vicinity. The most powerful nation minces no words in stating that the DPRK is the reason for having those troops there. The US has bombed the entire DPRK economy to dust, and has aggressively invaded Iraq, Afghanistan, Libya, Panama, Vietnam, Laos, Cambodia, and others since the 1950s. The US has sponsored coups and attempted to overthrow governments in Venezuela, Guatemala, Chile, Ukraine, Syria, Cuba, Nicaragua, South Korea, and throughout Africa.
The threat of overthrow by the US has also worked to keep the DPRK regime in power; in a word, the presence of a threat has worked to unify the regime. In many ways, the US presence keeps the DPRK government in power. Thus DPRK must keep the US boogey man in place.