I don't see the tragedy of the commons concern here. Presumably, each company is contributing because they need/want something with the kernel that is not alrea

I don't see the tragedy of the commons concern here. Presumably, each company is contributing because they need/want something with the kernel that is not already being provided. Instead of keeping the development in house, which would involve maintaining a fork and almost certainty breaking copyright, they decide to contribute it back to the mainline kernel. At the point where no one wants to contribute, I would expect that the expected value for some companies of having a single employee work on the kernel is greater than the That this happens to benifit everyone else is just a side effect.