His voters are rusted on. They dumped a great politician in Tony Windsor for Barnaby. He has the advantage of parading his role of Deputy PM, as if it has influence on getting thigs done for his electorate - but in reality, he does little for them. They are also spoon fed from birth never to trust Labor or the Greens, even though those parties would probably do more to improve their conditions.
For the above reasons, Joyce knows he has nothing to worry about, and can go on looking after his mining donors without risk of losing his seat.