Too be fair if someone sends me a pic like a nude or sexy picture with a face on it, I share mine.. just to keep respect and so they see me too. Feels also empty if I see a face of a wife, they don't see mine.. like yeah, it is also too show am I their taste or good enough? because I am not for everyone.. some are more direct too say, you're not it or I don't think you're ugly but not my type.
But in the other way I think what people mentioned, if you talk or DM with a couple / male whatever and want too go further than just fantasy, you wish too know the person or who he / she looks like. For me I like too see a face, just to get an idea.
I understand also the concept of privacy and that fakers exist or people get too see you which can be "used".
Hopefully my intake helps for you.