I'm going to guess they think if girls are watching it, boys aren't. Gaining 20% girls/parents might end up costing them 10% boys, which they presume might end up being a net loss for them.
He mentioned Cartoon Network specifically. On the other hand, Nick has fantastic shows for people of all ages and genders. I am a huge fan of Korra. A friend of mine started watching Avatar with her son a few years ago and told me to check it out. After Avatar ended, we continued to watch Korra and it is such a great show with strong backstories on almost all the primary characters. If I had a daughter, I'd buy her a Korra doll, video game, and craft supplies. I don't know why Cartoon Network thinks girls aren't profitable.