Moving to QT was a bad move because they abandoned something that was working for something that didn't and wasn't going to for years.
The whole cross-platform thing was a complete red herring and could not possibly make up for the loss of productivity. Even if GTK is non-portable, which it isn't, there is vastly more productive ways to solving that problem.
Another problem is that the toolkit is mostly irrelevant. GTK has warts, but so does everything else. No matter what you choose you are going to have to work with it and modify it to fit your system.
Application developers care about things like documentation and developer tools. As long as the APIs are not completely stupid they will tolerate it the same way that a guy driving a pickup tolerates the fact that he is driving a truck with white cab and automatic when he wants to have one with a white cab and manual transmission.
Customers care about applications and UI.
Changing the architecture over and over again served no purpose but to waste resources and time is a core reason why Meamo/Meego/etc failed miserably.