For example, in order to scale less expensively, the Great Firewall is architected such that it need not actively be in the middle of the entire flow of traffic and need not actively proxy. Historically, they didn't need it to do so in order to achieve their goals.
Now, however, the advancement of a combination of new technologies is finally closing that gap.
In order to maintain historic blocking capability it becomes necessary in the long run to actively MiTM all the connections.
But that can be made to scale and there are nations who can afford it.
How do we know? Because the job is not significantly harder than serving up all that content. (At worst it's a little more than 2x the work.)
And today most content is served up from a handful of privately owned infrastructures. If a corporation can build it, so too can a lot of nation-states.
The incentives to build this have changed.