Is Windows written the exact same way as Linux? Never underestimate the amount of technical debt that can be holding a team down.
We're comparing Linux and Windows, an operating system that contains 3.5 million files[2] (of course, not just the kernel in this case). That isn't really fair. Code is as perfect as humans can make it, and it certainly does not help that there's so much to take into account.
[1] http://hmarco.org/bugs/CVE-2015-8370-Grub2-authentication-by...
[2] https://arstechnica.com/gadgets/2018/03/building-windows-4-m...