Why won't Ponting retire?

Why don't sports persons know when its time to retire? By sports person I mainly mean Ricky Ponting. Is he too arrogant to see what others can see? The longer he goes on like this the more he will look like another old saddo "has been". If he had left when he could still hold his head high, he would be remembered, like Steve Waugh, as one of the greats. If he won't retire graciously, he should be dropped immediately and that would serve him right for thinking that he is better than he is. It's too late now to save face, because you will only be remembered as someone overpaid and under performing.