I think I made it pretty clear why.
I interact with this person every single day. We talk about a myriad of topics, she's never once mentioned a relationship, past, current, serious, not serious, that she's single, etc. I know that she worked as a waitress in a pizzeria during HS, I know that she went to an all-girls HS, I know where she went to college, I know that she used to do research on TB, I know that the town she is from is famous for steaming their hamburgers, I know that she has a cat, I know both her father's and mother's profession, I know her political beliefs, I know what musical acts she likes, etc. These are all things she's shared with me.
I'm sorry to hear you've never discussed anything personal with a co-worker before. Sounds like you've never had a friend. Usually in pleasant conversation, personal stuff comes up. "what'd you do this weekend?" "Went to a movie with my boyfriend, you?" "Wife and I went apple picking."
I met my wife at work. I know a lot of people who've done that. I think it's incredibly sad that you don't give a shit about anyone of the opposite sex that you work with. You sound like a sociopath.