There's the usual suspects in there (after a quick double check, it turns out microsoft.com just missed the cut-off with 140 commits, plus 2 from linux.microsoft.com, Amazon has authored 71, and alibaba have 139)
No one wants to maintain out-of-tree patches, it's a complete pain. Google was doing it extensively with the Android project for the longest time, but they've been working hard at getting those all in to upstream to drastically reduce the work involved in updating the Android kernel.
Keep in mind most of us don’t use our @fb.com addresses. LWN keeps track of companies by keeping track of who works where so our numbers are much higher than this list shows.
Applies across a bunch of companies (I use my IBM email but I know quite a few kernel devs here who prefer to keep their open source contributions under their personal email).
No one wants to maintain out-of-tree patches, it's a complete pain. Google was doing it extensively with the Android project for the longest time, but they've been working hard at getting those all in to upstream to drastically reduce the work involved in updating the Android kernel.