They're trying. And I appreciate that. Unfortunately it's still on-going in 2023.
"GTK+3 port officially done
GIMP 3.0 has been known as the GTK+3 port version, so you will be happy to read that this port is finally over. To be fair, we still have a few minor deprecation warnings here and there, but nothing like the hundreds we used to have."
https://www.gimp.org/news/2023/07/09/gimp-2-99-16-released/#...