two things I can think it's either for the girls to think about it or not but the same time they might think it's gross or some even belittle its size well lots of reason and I'm not a girl to even think about possibilities plus my line of work doesn't comes with mind reading and rationalization of girls way of thinking.
They say it's normal for a guy to think like that but I also can say that it might be normal for girls to think like that but they might be label as lewd and it's negative for them unlike for boys who take it as face value :heh
and didn't care much.