YA BOOK COVERS

I keep having a discussion with friends in publishing, and doing so right now offline, about how YA books with female lead characters almost always have the head obscured on the photo covers. I'm always told its so more people can identify with the character. 
If that is true then 
1-why have the lead characters on the cover at all? 
and 
2- why doesn't that happen as much with YA male lead characters?

YA BOOK COVERS