Why do men love full lips on a woman?

Not all guys do! Everyone is different. Some like fuller lips while others like thinner lips. To each his/her own. Same w/lip color, hair color, eye color, body type, etc. Anthropologists have suggested that certain body part variations are associated w/more successful breeding. What's important isn't what "guys in general" think or like but rather what "your guy" thinks & likes about you.