I think the main reason everyone calls out the Trek franchise's lack of LGBTGIA+ representation before 2009 is because the Trek franchise prides itself over being so forward thinking and progressive. They pridefully boast about having television's first interracial kiss (a claim which isn't even completely accurate) as well as daring to show a future where white people and non-white people are equal. If Trek really were as daring as its reputation would suggest, it should have been no problem to have a gay character by the end of the 1990s, and by the 2000s they were starting to look backwards because of a lack of any gay characters. Enterprise ended exactly one month before Doctor Who introduced its first openly gay character, after all.