It's more that in the past widespread surveillance required a lot of people, many of whom will have a conscience which will end up disrupting your surveillance.
The movie Das Lieben der Anderen makes this point very cogently.
Nowadays you can run a huge surveillance program with far fewer people, all of whom can be conscience free.
Im not sure how the next stasi will crumble but it'll be a lot harder to wrest them from power with the tools they have at their fingertips.
Whatever that limit might be is genuinely terrifying, given how far obedient soldiers have gone and not hit such a limit many times over the past.