I can understand why. The motivations and message are a bit deeper than WoK. But UC wouldn't have happened (in the same way) without WoK first, since I don't think Kirk had the same hatred towards Klingons before. Distrust sure, but not revenge level hate.
UC also has that connection with one of the best TNG episodes, Yesterday's Enterprise.
I will agree that those two movies have the absolute best soundtracks of all the movies.