It's not a co-op. They're just relatively small and mostly hire senior developers who demand a higher level of respect and work/life balance. They used to only work on projects people wanted to based on consensus and personal interest. People floated between teams, you were free to convince people to work on your pet project instead, etc. They stopped doing that when they started on Half Life Alyx and talk about it in the design booklet because it also meant that literally nothing ever got completed since there was no direction and promising projects floundered from lack of support.