I would put it this way:

Gtk and Qt are oldschool toolkits, which were developed for a time when the mindset was to make it as easy as possible for a programmer to throw a useful application together.

But we are living in different times now. To create a compelling (consumer-oriented) application, you don't just need a programmer. You also need a designer, someone who can develop not compelling functionality, but compelling usability. This person can be the same, but it does require a different skillset, and by extension, a different toolkit to work with.

Any programmer who lacks the required skills should team up with a capable designer. This has been a reality in game development since forever, but now it has also become a reality for application development (because expectations have risen).