Aengeuad parent
Various patches have existed for at least a decade but every time they're proposed some issue is found and they're not merged so the goal posts shift from 'just write your own patch' to 'just become a Gnome maintainer' with no guarantees that you'll get the assistance you need to implement the feature or whether it'll even be merged, and fair enough, the Gnome team really don't owe anybody anything, but in that case getting annoyed that the community keeps referencing a 17 year old issue is just a natural part of the exchange.
Maintainer refuses to merge bad work, shame on them?
If it was really bad work, then of course not.
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.
That's not subjective. When they merge code like that and then you disappear, they're now stuck budgeting time to maintain that API for years. They can't be expected to do that work when no maintainers care enough and no GNOME apps are even going to use that API (Status icons were removed from the GNOME HIG years ago)
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?