[NetStrikeForce]

Unconscious bias. They think they'll feel more comfortable with people that fit their own stereotype.

It's difficult to add diversity when you're unaware of your own bias, but you shouldn't be mad at the situation (in case you were). Think about it, do you really want to work in that team? You might want to also choose if you want to work in a company/team/project after interviewing - don't just blindly jump because it's Facebook. Their lack of diversity would be a big NO for me.

That's my attitude at life and it works. I live in a different country from where I was born, moved at an adult age so it's easy to tell I'm not native and, well, I look different than the local stereotype.