Why do guys think flexible girls are sexy?

okay well i just don't really get it honestly? i'm in yoga with a few guys (it's a school thing) and they all just ogle whenever i do something like the splits, or a very flexible seating position. and when i put my foot behind my head one of them got a ***** hah. i mean, i'm not even that indecent in yoga. like, leggings and a t-shirt. thanks <3