Because you simply do not know.
Regardless, I think both Kenny and Lilly are really flawed. I supported Ken in the drugstore and I thought he was a better leader, but because I didn't help him killing a dude before we were sure he was dead, he decides to leave me behind in Macon. I supported his idea of going to find a boat, but he bitches around when I say we need a plan B. At least he went with me when I remembered him I took care of Kat and Duck.
Lilly bitched me around when I supported Ken, but changes her mind after I tried to save her dad, then she goes psycho when I support Doug and try to make her reason and tries to kill Ben.