In a world without canaries, all providers could have received NSLs forcing them to cooperate with wide ranging surreptitious surveillance, and we'd be none the wiser.

Instead, we live in a world where we know that many of them either are not being forced to secretly cooperate; or in one where canaries don't work, and they're being forced to lie about it.

And of course, there are ways of implementing internal surveillance without the cooperation of providers: by trespassing on their infrastructure, by analysing and recording traffic at their border, etc.