If you grow up gay, going through high school thinking you are the only gay person in the world and hearing "fag" and "poof" etc shouted as insults about 1000 times a day, with the only opinions of gay people you hear being that they are sissys, transvestites or predators, and then seeing nothing but straight people on TV, in books, etc, when you spot a gay person in any form (in real life, on TV, in a book, in a magazine), they are FASCINATING.
Maybe because they don't keep their sexuality secret and you do, or maybe because they are shown dealing with the process of accepting themselves and you haven't done that yet, or maybe because they deal with it destructively and it shows you how things might happen if you deal with it destructively, or maybe because they are shown to act normally when you have always heard that to be gay is to be effeminate or ultra-butch.
When you get older and have been exposed to gay people/isues a lot you just like to see gay representation in media because you know from experience that when anti-gay straight people meet you and get to know you they may change their minds about gay people being evil and see them as normal, which makes it easier to get on in the world.
The same thing doesn't really apply to straight, white men because they have plenty of healthy role models all around from age 0, so I guess you wouldn't think about it much when you see a straight, white main character.