Or the guys just want to watch an anime girl with nice voice and cute model being a girlfailure, and have no interest in watching anime boys. They could've collabed all they want, and they would only have any kind of decent viewership during said collabs or when the viewers oshi doesn't stream. You can't grow a healthy fanbase by eating leftovers from someone's table, you have to find someone who would watch you for you. And unfortunately for them, the audience with the biggest interest in anime boys is fujoshi