This is because - somehow - it's gotten into people's heads that diversity is a GOAL. It's not. It happens when you don't care about differences but are willing to consciously overlook them.
We have had problems in the past with racial, ethnic, religious and sexual discrimination and - when people were willing to just say, screw it, he/she is simply the best candidate, they've done well. It's what happened when coaches realized that putting blacks on their athletic teams meant - WINNING GAMES. It's what happened when Hollywood learned that putting Asian martial arts on the screen meant - big bucks.
It IS true that people tend to look to people like themselves when forming teams, building businesses, making partnerships, adding employees. It's natural. In high school, I remember two girls given an assignment for the school paper to make a crossword whose answers were other students holding prominence in the school. The two girls were black - every single person in the crossword was also black, even in a school that was 70% white and they managed to overlook the school's star quarterback and running back, the student body president, the captains of every sports team and the current homecoming king and queen. Why did they exclude them? They didn't know who they were. Never occurred to them.
EVERYONE does this. But it's myopia. You CAN benefit from diversity. But it is NOT A GOAL. It just happens when you do go just on merit but make a conscious effort to do that.