How come I keep seeing?!

As a tendency, people like to know about themselves. Specifically, people want to know about parts of their body that might seem unattractive to others. Based on the nature of armpits (they have many hair follicles in which microbes can reside and are an area of the body with a lot of motion and rubbing), sweat, chafing, and other odor causing factors arise. My guess is that all of these people feel either insecure or worried that their armpits are unnaturally smelly and off putting because they do not know that everyone has similar problems.

because you secretly have an armpit fetish