This is mainly because of very different personality traits!!! Know it or not, the type of Music you listen to shows what type of personality you have. A psychological study was once made, showing the following results:
Factor 1 were blues, jazz, classical, and folk music—genres that seem to facilitate introspection and are structurally complex—and this factor was named Reflective and Complex.
Factor 2 was defined by rock, alternative, and heavy metal music—genres that are full of energy and emphasize themes of rebellion—and was named Intense and Rebellious.
Factor 3 was defined by country, sound track, religious, and pop music—genres that emphasize positive emotions and are structurally simple—and was named Upbeat and conventional.
Factor 4 was defined by rap/hip-hop, soul/funk, and electronica/dance music—genres that are lively and often emphasize the rhythm—and was named Energetic and Rhythmic.
See, Metal fans are Rebellious, while Hip-Hop is ummm... Whack