How do people only listen to one genre of music?

When people ask me for my music taste, I'll usually say the same three artists: Tokio Hotel, Evanescence, and Nirvana -- especially Evanescence and Nirvana because theyre popular -- but, in reality, I listen to a lot more.

Most of my friends listen to only one or two genres, and seem to hate music from any other genre, barely even taking time to listen to the songs before deciding they dislike them.

I don't know if it's normal -- I thought it was but I'm having doubts now -- but I like over 75% of music I hear, no matter the genre. There's always something in a song that I can like, like a single lyric, a melody, the instruments in general, etc. I think that's the best thing, because I can never run out of music to listen to, and theres always a high chance of me being able to listen to something new and have it become one of my favorite songs. In fact, I think it's harder to only stick to a few genres. So, people who do only listen to one or two genres of music, how/why?