I think this applies well to attracting and maintaining a talented and diverse mix of contributors: Safe spaces are important. I have seen the misogynistic and racist comments made in some open source communities, and subsequent dismissals when people point out the issues. I think that in maintaining a professional community there have to be strong standards on what constitutes harassment or inappropriate conduct. Of course, people can—and will—have a variety of opinions on what they should be able to express in open source communities, or any community. However, if community leaders actually want to attract and maintain diverse talent, they need to create a safe space and hold community members to high standards.
I also think that some community leaders just don't value diversity. It's really easy to argue that tech is a meritocracy, and the reason there are so few marginalized people in tech is just that they aren't interested, and that the problem comes from earlier on in the pipeline. They argue that if someone is good enough at their job, their gender or race or sexual orientation doesn't matter. That's the easy argument. But I was raised not to make excuses for mistakes. And I think the lack of diversity is a mistake, and that we should be taking responsibility for it and actively trying to make it better.