Ask John: Why Are Anime Theme Songs Sung in Japanese?

Question:
Why are most Anime Opening and Closing themes are sung in Japoanese?

Answer:
In commemoration of April Fools Day, today’s question is genuine, and presented exactly as I received it.

(Although it shouldn’t need explanation: Japanese songwriters and Japanese vocalists performing music for Japanese animation to be watched by Japanese viewers are naturally going to use Japanese language most of the time.)