First, I am not aware of any operating systems that are developed using agile methods, and second the empirical evidence is in that agile improves quality, so it would be better if they were.
https://www.amazon.com/Accelerate-Software-Performing-Techno...
https://en.wikipedia.org/wiki/No_true_Scotsman
2. And no, my position has nothing whatsoever to do with the "no true scotsman". I am not saying that they couldn't possibly be using agile because they have bad quality. I am saying that I am not aware of any of them using agile, and I was closely associated with at least one of them for a while.
And I also separately cite the evidence that has now been produced that agile improves quality, and conclude that if there are quality problems as you claim, a more agile approach would likely help, at least according to the empirical evidence.
¯\_(ツ)_/¯
What organisations need more than anything is open minded individuals that are not slaves to established dogma. The Agile manifesto actually says that all methods should be constantly re-evaluated to see if they fit the particular organisation/team. Your empirical "evidence" likely comes with a lot of context and is unlikely to be applicable to all organisations and/or domains.