All sorts of security features in the browser only work on newer operating systems:
Hardware-enforced Stack Protection: https://www.zdnet.com/article/google-chrome-this-new-feature...
Significant improvements to ASLR starting in Windows 8: https://msrc-blog.microsoft.com/2013/12/11/software-defense-...
And many more things. New Windows releases aren't just coats of paint.