Well, ok, there are a number of reasons. I can't give you a really technicall reason musically other than to say that the beat is symphatic or something like that which means it goes counter to our heart beat and as a result it causes heart problems by afffecting the beat of our hearts, if listened to for long periods of times.
2. It inspires feelings in us that are not edifing such as pride, or lust, or murder, or hatred, etc.
3. Plants exposed to rock music continually die. plants exposed to soothing music live and prosper.
4. The rock beat comes from african tribal demon worship. and it is the music of satan. Any african tribal worshiper of demons knows and recognises the rock beat as being his God's music.
5. The people associated with Rock music are evil looking, long haired men, tatooes all over thier bodies, drug takers, they commit suicide, like james morrison, the whole rock music culture is highly anit christian in scope.
6. Rock music in the church polutes the church and causes it to have less power with god, the more one brings into the church from the world the more a church looses power with God. Take for example, one that we can all agree on with, drinking alcohol in church.
7. The church up until the mid 70s was vehemently opposed to rock music and christians of that era regularly destroyed rock music they had when they got saved.
8. You can't understand what's being said most of the time in rock music anyway so the argument that the words are edifing is groundless.
9. Mostly young people, who don't have much experience with the Lord are pushing hard for rock music in the churchs.
10 Older people know better.
Well If I knew a lot about music i xcould give you some highly technical reasons, I've heard them but they were very technical and i didn't retain the info very well.
So I guess that's why. Probably other reasons I didn't remember. but thats a number of good ones above.