From my experience, there is a lot of software that will not build for platform older than 7/2008 due to missing APIs. Visual studio stopped support for xp compilation awhile ago. You still can use clang or such for simple programs today, but chromium is probably too complicated to port at this point.

I was curious so I found the bug where they tracked some of the post-XP cleanup work: https://bugs.chromium.org/p/chromium/issues/detail?id=579196

https://github.com/blueboxd/chromium-legacy exists for macOS, so it would only be fair if there was something similar for old versions of Windows. :)