It could be due to her being influenced by the cultural or social environment she is in. If such stories are prevalent in her social circle or the media she consumes, she might unconsciously become obsessed with them. Another aspect could be her own curiosity about nature or biology in a rather strange or unorthodox way, where the 'big cock' aspect is just a part of a larger exploration of the natural world, although this is a less common reason.
Well, it could be that she has a strange sense of curiosity. Maybe she's lacking excitement in her own life and this strange story about the neighbor has caught her attention in an extreme way.
A possible rewrite is 'Boyfriends' Inspiring Stories'. By changing it like this, we are emphasizing positive stories related to boyfriends, rather than the original phrase which was rather unclear and had inappropriate elements if taken at face value.