Agree some just end up with nothing and often go bankrupt after paying and don’t know how to react to as you say not being centre of attention with everyone cheering you on .And a sense of futility after a career is over. What do you do after the adulation of scoring an amazing goal against Chelsea when you receive adulation from thousands? Suddenly there is nothing.
On a more mundane level, it's why many many die soon after retirement. Their purpose in life has gone.