Kirito is very popular in the front lines and even the best of it. His popularity boost and pummel when his dual swords was announced and been beaten by heartcliff? (can't remember if it's the right name)
Plus all his harem girls are playing VRMMO games and met him in the VR world and not in the RL. And even if you meet him in RL. Kirito's looks isn't that bad. He is cute or more like girly in way (totally unlike a fatarse -_- character)
An ace and good looking guy plus a kind one. So what's not to like? They all fell in love with his mad gaming skills