The problem is that poor quality isn't the reason why they refuse. While not related to the file picker, I personally offered to port an important part of GTK3 to GTK4 (status icon support) and one of the maintainers told me flat out that he would not merge my work because "it was no longer in line with the direction GNOME is heading".
I suspect the real reason behind their refusal is purely subjective, unfortunately.
If you don't want to go through the trouble of becoming a committed long-term GTK maintainer yourself just to get this in, why not maintain that particular feature as a separate library?
Uh no. There have been at least 3 separate attempts at implementing this. One of them actually lives as a fork on github, and it works. None of them have been merged. The gtk devs don't care.
It should be annoying that the issue keeps coming up.
It's not a 'meme' that gnome lacks an extremely basic feature that is incredibly common in other GUIs.
There are many other issues with Gnome that actually is their decision and it is a problem. This specific one is a GTK issue. But for example their decision on window decoration in wayland is just wrong and makes the whole environment look weird[2].
[1] https://gitlab.gnome.org/GNOME/gtk/-/issues/233
[2] https://gitlab.gnome.org/GNOME/mutter/-/issues/217