Is it though? A much simpler explaination is that China - like any nation - can compel it's citizens quite easily to do something (carrot or stick). And tapping

Is it though? A much simpler explaination is that China - like any nation - can compel it's citizens quite easily to do something (carrot or stick). And tapping into/backdooring infrastructure a very effective approach. How do the Five Eyes governments know this? Because they were doing the exact same thing, with help from e.g. telcos. But most foreign telcos are somewhat well monitored, so attacking the hardware is the next logical step. There's no mystery here, it's just they can't come right out and say "this is how we would have done it", because they probably did.