Opening wpf window in desing mode in visual studio is not often desired. Visual studio doesnot have much tools to edit xaml in design mode. So most developers doesnot want wpf window by default in visual studio, but visual studio by default opens wpf window both in desing mode and xaml mode(splited window).

Opening in only xaml view  (dont let visual studio to draw visual elements on wpf windows) saves lots of development time. Since you dont have to wait lots of seconds till Visual studio renders visual elements.

Here are the steps

1. Go to  Tools-> Options
2. On options window

Tex tEditor -> XAML -> Miscellaneous

On the right side check <Always open documents in full XAML view>

See screen shot below.