There are a lot of really good female musicians and when you are a really good musician, you prefer to play with other really good musicians too and gender is not an issue.

Both my daugters play in mixed bands, one plays bass and the other guitar and mandolin.

The only time they have played in an "all girl band" was when they were really young. It wasn't a conscious effort to be an "all girls band", it was just that, at the age when they began, all their friends were female, the same as with "boys" of that age and as with boys, they decided, "Hey, let's make music".

I believe that the reason that there are so few all female bands is because there are even less female musicians, who believe making music with musicians of only their own gender is of primary import.