Andy,
It is nothing to do with lens quality. Its about lens flange to sensor plane. Roughly Nikon is 46.5mm and Canon 44mm.
I am also fairly certain the Canon mount is a larger diameter than Nikons so easy to make an adaptor as in your link, but not so the other way round.
Ignoring the electronic connections, if you were to make an adaptor for Canon lens to Nikon body then you could not obtain focus to infinity with that mount.
Worth mentioning, the mount in the link does not appear to have electronic contacts so Nikon 'G' type lenses will not function with it.
Don
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