More generally if you want to redact pixels, then don't replace them with information that depend on those pixel values. It doesn't necessarily mean a black rectangle, but that's certainly simple and it works.
My best guess is that, having seen blurring of faces (which is arguably OK when one merely wants to avoid casual attempts at identification, while retaining a ‘natural’ look), they assumed this was the proper way to do it in all cases.
Unfortunately, part of "leaving the visual interest behind" is precisely "pixels that depend on their real underlying values"....