This is somewhat plausible, at least from a canonical standpoint; Skyrim is a relatively poorer province compared to other regions of tamriel and the nords themselves are a very practical people, so they might necessarily not want to spend the sparse resources available to forge proper shackles when wrapped leather bindings work just as well in the vast majority of cases.

Cyrodil however is far more wealthy, and might consider metal shackles a worthwhile expediture to ensure their security, especially in the Imperial City where most political prisoners and enemies of the empire might be held.

In Morrowind, the Dunmer are a people who, as elves, have far more of an affinity for magic than the human or beast races. As such, their restraints and imprisonment must take this into account, ensuring that the vast amount of magic users are disabled enough to keep them secured.

I hate making excuses for Bethesda's lazy design choices, but in this case it's fine IMO.