[kitsunesoba]

I don't think it's necessarily an error to reimplement widgets, with a caveat — the reimplementations need to be good. Really good, at least as good as native widgets and preferably better. An example of this is Sublime Text/Merge, which feel excellent despite being built with a bespoke UI framework.

This rarely happens though, and I wonder if it may have to do with the limitations of the technologies often chosen to do the implementing with, or if it's more of a philosophical thing with the projects in question not holding themselves to high enough of a bar.