I consider the following as possible reasons:
1. GTK+ is completely (GNOME) community owned (QT is a company owned, which companies like to avoid)
2. QT is LGPLv3+/GPLv3+. This, I assume, is to encourage buying commercial license than promoting free software. GTK+ is LGPLv2.1+, a lot of individual/small team developers prefer [L]GPLv2 over [LA]GPLv3.
3. Accessibility is pretty bad in GNU/Linux in general. But if there is one, the only choice is AT-SPI[0]. It's a GNOME project. I think KDE is a bit behind (I'm not sure though).
4. GNOME, GTK+ are GNU projects (Or many people prefer GNOME because it's a GNU project). I have seen many people in our Free Software User Group using GNOME just because of this.
> Gnome is approaching a crisis point, stripping away features as the debt comes due for bad design decisions made
We have seen a lot of software pieces whose development stalls, just because the code complexity increases way beyond some limit, or the main developer quits. Many (vocal) users prefer well configurable software pieces - but it comes with a high price. Many implement every possible feature to look the application c00l. But eventually as we gain experience, we may eventually abandon the project just because it's bloated (code wise), or even re-write it with less features, so that the code is more maintainable. If we look the code of many abandoned projects, we can see how bloated the code is, with many hacks, and bad designs.
I think GNOME is in the path of porting their applications to maintainable pieces, and eventually adding features as the code gets better.
[0] https://en.wikipedia.org/wiki/Assistive_Technology_Service_P...