Because then they don't have to include the ability to configure wifi, which (while not that hard) is one more thing to do and for a hackathon that's not really contributing to the end goal.
Once I got it working it felt really cool though. As a user I don't want to configure WiFi on the microcontroller at all. I would be really cool if I could walk up to a 'smart device' and set my phone next to it and do zero configuration.
I am curious about adoption and features that would make big difference to users :)