Short version: Because everyone has an opinion and they are entitled to it.
Long version: Because music is pretty much the most subjective form of art there is. There are so many different forms of music that it's impossible to like all of it, and if someone doesn't like mainstream music because it doesn't suite them, let them not like it. You do get people you hate anything mainstream simply because it's mainstream, but these people don't really have a leg to stand on, logically speaking.
To say that one must like mainstream music because they like mainstream movies is absurd. They are completely different art forms. It's like saying "Oh, you enjoyed Ed Wood? You would like '...and Oceans', because they're both obscure."
Long version: Because music is pretty much the most subjective form of art there is. There are so many different forms of music that it's impossible to like all of it, and if someone doesn't like mainstream music because it doesn't suite them, let them not like it. You do get people you hate anything mainstream simply because it's mainstream, but these people don't really have a leg to stand on, logically speaking.
To say that one must like mainstream music because they like mainstream movies is absurd. They are completely different art forms. It's like saying "Oh, you enjoyed Ed Wood? You would like '...and Oceans', because they're both obscure."