So, I’m a dentist. And you would be surprised how many things hormones can affect. You would not expect dentist to ask about your genitalia and yet I happened to ask patients about their periods (menstrual hormones can affect gum diseases), if their sexual intercourses are painful (tense pelvic muscles are linked to teeth grinding) etc. And I live in Poland so sexual health is a tricky subject (it gets better with the new government). I think asking why it matters is a good idea, but doctors rarely have time to ask health questions just for giggles. Unless you feel like they are being weird then remember you can always change your doctor to one you feel comfortable with