I would mildly contradict that. There are shows which touch on the subject, however briefly. What annoys me about the treatment of the theme in mainstream entertainment is that whenever homosexuality comes up it is a story gimmick. I don't know of any series or movie with homosexuality in it that doesn't make a big deal out of the fact that two persons of the same sex have a romantic relationship. Gay people on comedy shows are usually unbearably placative, gay people in dramas usually suffer until their suffering is resolved and we're treated to some unctuous morality lesson. Is it good that the topic isn't a total taboo anymore? Yes. However, being gay is not treated as normal, not even when the overall message about it is a positive one. Homosexuality gets thematically singled out as an interesting plot point, something that is always emphatically noteworthy. To me that contradicts the naturalness of being homosexual in a way.
Does that make sense?