Because in Apple's case they are merely using Linux as off the shelf server software to serve a website or maybe files in their HQ. They have no need to modify

Because in Apple's case they are merely using Linux as off the shelf server software to serve a website or maybe files in their HQ. They have no need to modify Linux therefor they have no need to create patches. Apple doesn't even contribute to FreeBSD despite lifting many components for OSX AFIK. The others have deep investment in Linux and therefore contribute patches.