[ImpactBreaker]

Well, there are several reasons why people mock japanese music.

-The most ignorant people who have absolutely no clue, associate the word "japanese music" with old traditional chinese music, and even whistle something they've listened in some traditional tune, from some cartton or movie that joked with it. The fairly ignorant people associate japanese music with enka.
-Some people associate japanese music with otakus -crazed nerd obsessive anime fanboys- who live entirely for cosplaying and swear they're truly Shinji Hikari from Evangelion, so they think: "ridiculous people => ridiculous music"
-some people prefer their local music, and can't understand why people will look for stuff they can't even understand
-The people who can actually go through all of those barriers face yet another one: associating japanese music entirely to ai otsuka and morning musume, a.k.a - Cute, nasal, annoying music for female children.