Themeing was a scouge of the Windows 9x age that developers had largely given up on and the support for theming in WPF as part of the backlash against what people perceived as visual excess.

It was fun for me to see this "visual excess" at work years later in the 2-d graphics of games written against Sony's PhyreEngine

https://en.wikipedia.org/wiki/PhyreEngine

such as

https://en.wikipedia.org/wiki/Trinity_Universe_(video_game)

Even though people hated Vista, the WDDM model that it brought in is one reason why Windows crashes much less than it used to and why GPGPU computing is a thing. Someday Linux is going to switch to Wayland or something else like WDDM.