Contrast that to FOSDEM, which is completely different. This isn't just an offspring of early hacker culture. This is as offspring of how "socialist" european university systems were.
A lot of bigger OSS projects were started during peoples university time and what's so fundamentally different between how universities in Europe were before? You didn't have care about graduating. Some people stayed in University for 10 years, it was free and sometimes even had some benefits, like cheaper healthcare.
Now studying forever subsidized isn't always a good thing, but it has some nice side effects, like being able to work on your side project without having to worry about your livelihood(something that is unthinkable in the US).
The European higher ed systems has gotten more and more close to the US system with the Bologna process[1].
Most Americans immediately think about how to monetize things, and don't get me wrong, being able to live off of your open source project is nice, but it wasn't the focus in the past.