Since BLs are gay, they are more socially deviant already and therefore likelier to both realize their non normative orientation and seek to express it through community forming.
Since GLs are straight, we are less socially deviant and therefore less likely to associate ourselves as non normative or try to form communities.
A BL who likes also adult males is still already socially deviant. A GL who likes also adult females has socially acceptable partners.
Of course I'm talking about males. But it also seems that female pedophiles are rarer than male pedophiles; and that contact is more acceptable in adult females, as mentors and guidance figures, in light physical contact and even in full on sexual contact. Again this would act against community forming.