Why are fans so bothered by English releases but not Japanese releases?

One issue that has always puzzled me since I became a K-pop fan is the apparent disdain for songs released in English, while those released in Japanese are widely accepted. When a group or soloist releases a song in English, accusations often arise that they are "Americanizing" or "losing their Korean roots." However, when they release songs in Japanese, it is considered normal, and you rarely hear criticism that they are straying from their Korean origins.

So why is there this difference in perception? What is the dividing line that makes English releases seen as a threat to authenticity, while Japanese releases do not generate the same reaction?