I think part of the answer to your question lies in the origin of the "import" designation. It is illegal to employ somebody based on their country of origin / citizenship - which makes Canadian Content rules very tricky. So "import/non-import" was designed and determined by where a person originally received their football training. Instead of Saying American / Canadian... which teams and the league could not legally do, ever.
Josh Bartell the kicker made it into the CFL as a "non-import" because he had not received football training anywhere in North America, and has been grand-fathered in under the new CBA. I think this was a real stretch of the rules in the first place, considering that Australian Rules Football League players receive monetary compensation. To say he's not trained, and not a professional must have involved some genius grey-area logic on his agents behalf... anyway, I love seeing the guy play.
I think "National" and International go along the lines of further legally defining where a person is trained, and not their country of origin, or citizenship. (circa 1960's, where American players would be counted as "Canadian" once they obtained Canadian Citizenship). There are also current players who are American citizens, but spent enough time in Canada to earn "non-import / national" designation.
Finally, to answer your question with another question; Why not have some more "National" pride? Us Canuckle-heads all too often downplay or dismiss our own culture and heritage, and in our Canadian Football League overall i think "National" is a much more suiting, and pride leveraging thing than "non-import"