What would you propose those speakers do differently?
A follow up question: why do you say that would be more effective than what they did?
(And, I would ask you, is that something that still maintains their commitment to diversity, since they all mentioned that was more important than speaking opportunities?)
I always find in life that you get better traction when you approach people with a solution instead of just a problem.
So perhaps they could've said "Hey, I think it'd be good to increase speaker diversity, and I really recommend person X, she's amazing at Y, I could approach her and ask if you'd like?"
Instead of just yelling "There's not enough women!"
I hope other conference organizers take note and work to improve diversity while also actively avoiding speakers who pull stunts like this.