Because it's more complicated than that. People just want to make everything simple. But love and sexuality are complex subjects. To me it's universal because it's an amazing love story above all. Ang Lee never said that it was bad if it was called a gay movie, he just said that it can be discussed. And it can.
hes saying that this IS a gay movie and that IT IS UNIVERSAL. WHAT HE DID WITH THE LOVE BETWEEN TWO PPL SHOWS HIS KNOWLEDGE ON THE HUMAN HEART AND IT CHANGES OUR UNIVERSAL PERCEPTION OF A MAJOR PART OF LIFE.