I don't think there is "a problem of one very odd choice of permanent BGM".
(this is just a subjective opinion trying to be sold as an objective fact)
Because what the op calls an odd choice and a problem, is one of the most brilliant musical themes for a zone this game has ever had (in my books). And from what I've heard a lot of other players also appreciate this beautiful song and this very unique BGM.
At the end it's just a matter of taste... and as we all know, tastes differ.
Not everyone will like every BGM of every zone. There are some zones in this game, that have a BGM that I absolutely dislike (or find highly annoying).
However I would never think of demanding a change just because not every BGM is tailored to my very personal taste.