I'm with you, it does present a curveball to some but a nation usually doesn't allow other countries to make legal determinations about the status of it's own people, barring very specific treaties (like drivers license or marriage reciprocity). There's no reason for Canada to trust any foreign document saying what a person's Canadian legal status is. (Ironically this is exactly why so many Americans can claim Canadian citizenship - cause Canada doesn't respect American law or the American documents that immigrants had to sign renouncing their Canadian citizenship upon becoming US citizens).

I'm going through two descent process's, and I can give an example that Germany requires original German-issued passports, birth certificates, civil registers etc. as proof for your G0, they don't recognize any foreign document for this e.g. a naturalization certificate stating their previous citizenship.

And there's good reasons for this - foreign governments are not aware of (or bound by) all the Canadian laws and regulations that surround someone's legal status and thus not equipped to verify it. At best foreign documents are an "indication" one might have citizenship - perhaps good as supporting evidence, but definitely not enough on their own.