The team at Microsoft that was working on it probably got put on different projects. There wouldn't be anyone to put in the effort to get the code cleaned up of any proprietary libraries, internal references,.. No way they are shifting people back around and paying for development to get this done.
FYI there's an open-source project "Monado" which attempts to reverse-engineer inside-out tracked headsets. At the moment their WMR support looks promising, headset has 6-DoF tracking and just recently controller tracking has been figured out.
Said progress will trickle down to the Oculus Rift S as well
Sure? No. It was silly of me to suggest it was a question of motivation. I don't know enough about it to make any such assumptions.
I did however give it another go earlier this year, with no success. I could try again if there is reason to think it should work. Valve is the company I respect the most when it comes to caring about Linux. Which is why it always surprised me that I couldn't use the Vive there. Still one of the very few reasons left for dual booting.