> I admit, I do not understand GTK/QT development model at all.

It's very easy to understand.

QT is a commercial and de-facto proprietary product and the development model is: do what the paying customer wants.

GTK has no customers and after it was taken over by the GNOME crowd the development model is to deliberately sabotage the FOSS ecosystem. Small long tail projects can not afford to follow the relentless stream of backwards incompatible changes produced by upstream and die off. Even big projects like GIMP struggle with this. The result is a broken ecosystem which serves certain market participants (e.g. that offer desktop operating systems) very well.