Because you can write web applications without having to use crippled, half baked JS frameworks. GUI programming was solved over a decade ago. The things we do in the browser these days, in terms of complicated web apps, mostly consist of reinventing the wheel. Backbone, ember, knockout, etc are all toys with missing wheels in comparison to a serious GUI toolkit. In contrast, Qt is well tested, very well designed and elegant. It's been around since 1992 - 21 years old!
Porting 'legacy' QT apps with too much functionality in the QT bits to a browser hosted environment could, I imagine, form a case in favor of simplifying software delivery. (That, or forcing a desktop upgrade to i7's. Think of the kickback opportunities!)