Or most of them probably just gave up making GTK themes.
https://github.com/QtCurve/qtcurve-gtk3 https://igurublog.wordpress.com/2012/11/05/gnome-et-al-rotti...
For instance, they've deprecated GtkStatusIcon in favour of AppIndicator: https://bugzilla.gnome.org/show_bug.cgi?id=734826 What's wrong with freedesktop systray?
Gtk3 is really becoming isolated and gnomish-only. Frenzy. Mozilla's transition to gtk3 now looks completely catastrophic in a long-term perspective.
Yeah, things are pretty terrible for theme developers. It's like GTK 3 development was steered by Steve Ballmer.
With GTK+3 you do everything with CSS alone.
Of course full stability cannot be provided due to the fact that the CSS can poke at the internal composition of composite widgets, not unlike how greasemonkey scripts can hardly cope with the target website changing, but things got much more stable in the last few cycles.
Meantime, clunky, terrible C modules written back when GTK 2.10 was a thing work just fine on 2.99.
That is not simplification. Simplification is when things get easier, not when they get harder.
I reiterate: full stability for theme developers CANNOT be provided, unless you're willing to give away much of the power of the current theming system, basically going back to the annoyingly limited pixmap engine. This (understandably) is not a tradeoff the GTK+ developers are willing to make, and I guess neither third party developers.
> Meantime, clunky, terrible C modules written back when GTK 2.10 was a thing work just fine on 2.99.
I don't know, I remember Murrine being often broken after new GTK+ releases, despite it being under active development.
> https://github.com/shimmerproject/Numix/issues/206
That issue has been opened on 10th April, I guess your issue is more than your theme needs more help for its maintenance rather than GTK+'s fault. Again: there's no provision of stability for themes. Either you accept to keep up with upstream or you'd better stick to the default theme. Just like using a greasemonkey script when a website changes.
The changes in GTK+ have become progressively less dramatic: this means that fixes for themes are now smaller/simpler, not that they don't need active upstream tracking.