And Silverlight and WinRT. I still don't understand why they couldn't keep developing WPF instead of shipping a new framework every 2 years.

Pessimistic answer:

Ever seen that joke graphic with the org charts of various tech companies, where Microsoft's is a bunch of nodes with little hands sticking out and pointing guns at each other?

WPF was a product of the .NET team. WinRT was owned by the Windows team. The two have had a rivalry that's famous for producing collateral damage.

Optimistic answer:

WinRT was designed to be consumable from many languages and platforms, not just .NET. They preserved as much as they could (e.g., xaml), but you can't rewrite the core of a thing without a few growing pains.

Typical MS roadmap schizophrenia. Honestly I maintain some WPF hanging out of the side of a product and I wish I had built it in winforms now.