Well most of Apple's servers and services run on Linux and there is clearly a demand for Linux laptops from developers. If Apple has to be friendly with OSS supporting Linux will take them a long way - good for developers including Apple's own services/infrastructure folk, broadens up the Workstation market again for Apple etc.

Doubling down on Open Source is not really doubling down if you just continue to dump code on github.

I think your definition of open source is much different than mine. Requiring cooperation or interaction with the community is very GNU / GPL mindset, not BSD. Many of us are perfectly OK with code drops.