As someone who develops and tests recipes for a living, it’s literally my job to describe how and why certain flavor pairings work. Usually, that’s a relatively attainable task, but sometimes, when faced with this particular why? I can’t think of a better answer than: Just, because!
Think about pork and brown sugar. And seafood and butter. And beer and sausage. And of course, chicken and vinegar. They just…work. These combinations have been around for a long time, in countless cuisines, yet are also constantly revived in new recipes.