Government has a mandate. That's how it can function. They have evidence, why reveal it to the public (and thus china)? I grew out of my Ron Paul phase at 15.
You trust China over your own government? Move then.
You trust China over your own government? Move then.
I am old enough to have seen several instances where organizations had internal reasons for their decisions and chose to argue something completely different in their outward communication. Given that an exclusion of Huawei had the obvious side effect of protecting domestic markets, this leaves quite some room for doubt around this specific instance. You say it yourself that governments have mandates.
From that perspective it makes a big difference whether the Chinese have mostly secure back-doors or their software is just generally insecure.
https://www.cbc.ca/news/canada/ottawa/rcmp-chinese-police-st...