To be clear, I'm not making accusations about Vietnam, I was just thinking about it and found it a little strange.
I can think of some fairly plausible reasons, but just because those reasons are plausible doesn't mean they're actually correct, so I was wondering if anybody had a more concrete historical and materialist understanding of the situation.
I don't think anybody thinks that, certainly not here?
The OP's question was "why does Vietnam have a relationship with the USA and the DPRK doesn't" and the history of tensions with China is the reason for the faster-than-expected renormalization of relations