WPF was atrocious from the beginning and Microsoft absolutely did the right thing by not basing everything in Windows on it.

Every WPF program was laggy and took ages to even start up (is everyone forgetting hard disk speeds?), partly due to it being managed code. The components didn't feel native either, and the coupling to managed code and garbage collection basically ensured all those would be perpetual issues. Yeah the programming model was beautiful and all, but you're supposedly developing to make your customers happy, not to make yourself or computer scientists happy.

You can see how terrible it would've been to base Windows's shell on WPF by looking at how much users have loved the non-Win32 windows since then.