There's been tons of female oriented films such as Barbie and Bratz CG films
to come out, but most are direct to DVD. Hoodwinked was about Little Red
Riding Hood. Happily N'Ever After also had a female lead. And if you look at
Western animation overall, it tends to feature females as the predominate
leads. (Snow White, Cinderella, Little Mermaid, etc.) There's no shortage of
animation for girls. (Anime tends to be very mixed between boys and girls.)

Some of it is due to the market and some is due to the story itself. Nemo
just wouldn't work the same if it was about a mother looking for their lost
child. Some of it is due to market. A movie about cars is designed to appeal
to boys so it needs a male lead. And girls will see a movie with a male lead
but few boys care see a movie with a female lead, mostly because they tend
to be romances.

Some of it is simply due to the nature of the technology and who has been
producing it. Most of the CG we've seen has been by Dreamworks and Pixar.
Don't forget, it's only in the past couple years that there's been an
explosion in CG animation. As the industry matures there's sure to be more
of a mix.