The thing is OP that people generally post threads in gender neutral language for 2 reasons: 1. They are men who think that they'll get harsher comments if women know that they're men, and 2. People who don't think the sex of the participates is relevant and want to prevent the replies being biased along those terms.
Generally, but not always, it matters in discussions around sex if you are a man or a woman posting. That's because men have a long standing history of demanding sex with no regard for the feelings of their partner, whilst many women will refuse sex for valid reasons. If you are a man posting "my wife never wants sex" you will quite rightly be asked whether she is afraid of getting pregnant, recently postpartum, experiencing low libido from breastfeeding, "touched out" from doing most of the childcare, or exhausted from doing most of the housework. These are very common reasons women don't want sex, and they often occur against a backdrop of the man being lazy, pushy, unempathetic, and sexually entitled.
If a woman posts "my husband doesn't want sex" it's less likely that he's tired from all the housework, and more likely that he's stressed at work, watching too much porn, depressed, having an affair, or that there's a medical reason. People post neutrally to avoid these "sexist" assumptions, but that doesn't help when they also happen to be true. Men and women often live very different lives, and the power dynamics between them are especially important when it comes to sex.
By posting in a neutral way people assumed you were a man trying to avoid the above allegations, and responded to you accordingly. When they found out you were female they realised their advice was unlikely to be relevant. People wanted to give you advice that would actually reflect your situation, and you kind of wasted their time by making them play 20 questions to get a crucial bit of information. Maybe you didn't think it mattered which sex you both were, but sadly that isn't the world we live in.
Tl/dr: sex is a gendered issue, so using gender neutral language to discuss it will lead to meaningly generic advice.