I think they are making the assumption that if such a govt backdoor existed, it wouldn't be used for generic mass spying, but instead targeted at specific indiv

I think they are making the assumption that if such a govt backdoor existed, it wouldn't be used for generic mass spying, but instead targeted at specific individuals they are trying to find/arrest. That may or may not be true, but I feel like the former would be a whole lot harder to hide, and the risk of having to reveal it in court would likely mean they aren't going to blow their cover over someone who wasn't worth it.