They already know and don't seem to mind a lot. They just disable all VPN traffic, etc during sort of special political periods e.g. Tienanmen square events anniversary.

It is probably better for the government to know how it is done so it can be stopped at will, rather than the people in question constantly finding new ways.

There are always some people who try to circumvent their censorship, and it is not worthy of their time trying to block every one of them, as long as the majority of people are properly confined.

Well, that is my speculation. I never get into any trouble for breaching the firewall.