The GTK bindings are being used pretty heavily by a few GNOME projects now, so I would expect them to continue to get the maintenance effort.
It's a heck of a lot easier to bind to an existing GUI library than writing the equivalent of GTK from scratch. But all languages have this problem, and most of them don't have Microsoft's ability to generate multiple different and incompatible GUI toolkits to suit the fashion of them time.
As others have already mentioned in the thread, they didn’t kill it, it is just not compatible with GTK4 out of the window. But a similar program for that is being done.
It's a heck of a lot easier to bind to an existing GUI library than writing the equivalent of GTK from scratch. But all languages have this problem, and most of them don't have Microsoft's ability to generate multiple different and incompatible GUI toolkits to suit the fashion of them time.