Hi Dillhole
The decline happened over a large number of years. Every year losing 25 points or so
rating points and then it was suddenly 100's. before they levelled off around about 1400.
A lot of players I grew up and with still alive stopped playing about 20-30 years ago
when the silly blunders started sneaking in. It was not the fear of losing but not being
able to maintain a high standard.
@Schlecter
I think the problem could be answered one way, assuming no biological problems are present, with an Indic perspective. When you have played all your life, naturally, the desire wans because you have satisfied that desire, and/or you have come to realize that you have nothing to prove to anyone anymore, not even to yourself. When you realize that you are not your body, not your mind, then you might have to find a different reason for playing chess (fun rather than trying to score) or quit altogether.