The GNOME stylesheet is not GNOME-specific? Tell that to elementary, that they need to throw away their own stylesheet and adopt Adwaita. Or to xfce. Or to MATE, Cinnamon etc. Granted, they are still on GTK3 but same idea.
Adaptiveness - ditto. Do you see elementary, xfce etc using it?
then the whole Gtk is gnome specific. And also libadwaita apps are being used on non gnome environments, just like gtk apps.
I mean there are plenty of things in GTK that are indeed GNOME-specific and wouldn’t have been added to GTK today - e.g. GtkShortcutsWindow, the current GtkAboutDialog layout, the current GtkMessageDialog layout, the current GtkFileChooserDialog layout etc. All of those things people from those environments always complain about.
Did you know Granite provides a custom MessageDialog because GtkMessageDialog doesn’t work well in elementary and can’t be made to work well there, for example?
And also libadwaita apps are being used on non gnome environments, just like gtk apps.
Libadwaita apps such as GNOME Contacts, GNOME Clocks, GNOME Calculator or GNOME Characters? As well as third-party apps made for GNOME and following the GNOME HIG such as Shortwave or Amberol? Sure, they can be used anywhere, and?
Meanwhile e.g. elementary apps such as Pantheon Files, elementary Code and third-party apps like Planner or Dippi - they are using Granite, elementary stylesheet etc instead. And they can be used on GNOME as well.
“gnome” is not a person. The developers of GTK and libadwaita are not the same. But that doesn’t matter, you are still missing the point. GTK is used by GNOME, also elementary, xfce etc. It’s not a GNOME-specific library. libadwaita is. End of story.
You may want to read the announcement blog post, for example, it explains the specific things it’s solving quite well.