Wow I didn't logged in for a while and you came with a lot of interesting points!
I also think language is a main issue. Most of people enjoy music for entertainement but a few are real music lovers, and then the most of listeners are only used to english music and his/her native speaking. Understanding lyrics are not something important in my opinion, many people listen to english music without having an idea about what it means. It is mainly about "pleasure" to the hear because they are used to.
I find it very sad to read stuff like "Frankly, it's not really their business what I listen to anyway." ... Music need to be share to everyone and, with a bit of luck, sharing j-music could reveal new tastes to someone. But I can't blame you because I don't really share to other about J-music. Hearing bad thoughts "forced" me to mostly share more mainstream music, even if I listen a wide variety of types of music.