I think its cause boys start puberty a little later than girls most time so you have a freaking out 9 year old girl and then a confused 13 year old
Also I could be very wrong but I think puberty is a more taboo topic for girls over boys. From adults, at the very least. Puberty in general is also a taboo topic. But if ONE BOY understands it and tells kids, EVERYONE OTHER BOY WILL START JOKING ABOUT IT-
The script is flipped where you say they wanna talk about it more. They most indeed do not SO THEY DUMP IT ON HERE