I agree with orenji -- if they use english words here and there it might make their music appeal more to those who don't know a word of japanese (e.g. me
) Thus, non-japanese-speaking fans have a very random idea of what the song is about, and we are able to speak about the song/spread the word (rather than trying to pronounce a song name in a language they may not know a word of or be able to read)
hope that makes sense...