From the same release with release countries “United States”, “Japan” and “Taiwan”, the latter is chosen even though my preference is Japan. All three have the same match score, so I’d guess it should use preferences like this.
The disk linked here.
Preferred release country not functional?
The preferred country is used to give a btter score to releases that contain a release event for your preferred country. So your linked release would get a better score than another release because it contains Japan as one of its release events.
But customers often want to use the release date with the earliest release info even if its not their preferred country, I think this is what you are encountering. Make sure you set Preferences/Musicbrainz/Format/When selecting year and country of release prefer to use to Country not Earliest Release Date