To offer another perspective.
I'd say the W3C wasted a huge amount of time pursuing quests of purity (XHTML) over actually making the web better for users. I see the value in what they were trying to do, but it wasn't letting people do the things they wanted to do on the web.
As browsers started just implementing features outside of standards in completely disparate ways because everyone was desperate for them (leading to plugin hell, apps rather than websites, etc...), WHATWG was created to try and ensure that the web remained a single thing and not a mess of things that would only work in one browser.
The web platform sprang forward massively as a result of this, with browsers implementing much more consistently and with new features tending to be implemented in compatible ways, with real progress being made.
This lead to the W3C specs becoming totally redundant and the only way for W3C to keep up was to lamely try to copy from WHATWG into a "spec" at random intervals and claim it was something people could work towards, when it reality it offers no real advantages over working to the living standard, because no browser offers better coverage of that spec than any other random point of the living spec.
People want features. We saw what happens with a very slow moving, rigid standard: plugins. Flash was popular because at the time you simply couldn't do good video, animation, games on the web platform. Likewise, mobile phones shifted to apps because websites couldn't do notifications or use location information. You can bemoan a living spec, but you get one anyway, because people will work around the web if they can't do what they want. If you want to use a subset of that living spec, use it, but at least keeping it together and agreeing on roughly how to do these things is better than plugins or abandoning the web entirely.