Maybe that's one of the keys to LeBron unpopularity, he has very masculine face nothing boyish/effeminate to it.
Compare him to Kobe, Kobe has more delicate features which might make him more likeable on some subconscious
level. I am also quite sure Kobe has more female fans than LeBron. Maybe some men identify him on some tribal level as a threat, big guy with neanderthal features who can kick your ass. It may make him come across as unfriendly compared to charming Kobe Bryant, ever smiling Magic Johnson or babyfaced Eric Snow.
tldr people like kobe, not lebron coz lebron is ugly