It's not only culture, it's also mutually beneficial, the cost of maintaining a forked version of the kernel is not worth it. Meanwhile working on a patch and p

It's not only culture, it's also mutually beneficial, the cost of maintaining a forked version of the kernel is not worth it. Meanwhile working on a patch and publishing it upstream is relatively easy "fire-and-forget", the patch is there, other people will use it and contribute back. Companies still have a ton of private code that never makes its way into the open source world.