Broadcasters themselves aren't subject to pre-clearance; obviously, live TV exists.

> the most the government can do is stop you from repeating it and punish you for having done so.

Yes - and, because of this, Clearcast exists with a sort of "TSA pre-clear" role. If Clearcast pass it, it's very unlikely to result in subsequent legal action.

TV stations are in principle free to broadcast unrestricted ads live and deal with the consequences. Obviously, they have no interest in doing that.