The reality is that they didn't work hard enough to find good quality presenters that represent the actual world we live and work in - one where people approach problem solving in myriad different ways that stem from their own history and experience.
tl;dr - if you can't find women, POC for your conference, you didn't look hard enough.
Part of the problem with finding more women and/or POC is that most conference organizers aren't looking for people at all; rather, they're looking for interesting projects/products/businesses. And what happens is they get a representative of that organization on the phone who agrees to send someone to present, but often they don't even know who will actually be getting on stage until much later.
This obviously isn't true if you're getting a keynote speaker to talk about their career, but you only get one of those per event.
Then take one considered magically good, like Strange Loop. Their excellence translations into excellent diversity work too: (http://bridgetconsulting.com/?p=131)