Earlier quoted context omitted.
Who is to say that any ransom demand would have been made publicly? It may well be that one has been made but that we just don't know about it.
The hijackers would probably want to make it public. It's an insurance for their safety right now. A government might simply bomb the parked aircraft and blame it on a crash or the hijackers.
Besides, if they knew where the plane is to bomb it this would be a hostage situation right now. They might be in a country which wouldn't welcome the incursion but I can't see the Chinese being overly bothered about that given the number of their citizens on-board.