Disclaimer: I don't know this personally, just going on what I heard on a podcast. My understanding is that these events they host are sort of like conference

Disclaimer: I don't know this personally, just going on what I heard on a podcast. My understanding is that these events they host are sort of like conferences where they find some space and get hackers together for hack fests and to build stuff. It's collaborative and while they don't pay the devs, they have expenses. I don't know how good the ROI is, but it's certainly an interesting model.