And I haven't done Hancock quest, I never had him as companion. But I understand why he would be popular and desirable for girls. Only for two things: Confidence and Power.
The guy has enough self-esteem to compensate for every misfortune in the wasteland, and he's nothing less than the [censored] leader of his own city. A popular man who has everyone bowing to whatever he says is not seeing as a loser junkie, he's the epitome of success in the wasteland and in our world too. So he's not the junkie you see on the streets, he's the superstar ultra famous important man who dies of overdose. Not to mention girls has something for bad boys, despite constantly complaining that everyones treats them bad, girls love bad boys a lot, and Hancock is the badass rebel that steps into the bully that's picking on you to kill him, don't you think any girl would be incredibly wet at that moment?
I also understand why girls would feel atracted to his name. So yeah, he has everything, everything except a pretty face, but that's how girls work, Hancock acts like he has the bigger dike and it clearly has an effect on girls because they know what's really important.
Now compare him with Cait, and you will see why Cait has really nothing to offer or to compete with.