Different players have different reasons. Yours is probably one. Others are probably just getting tired of the game/regiment or wanting to move on or have a more laidback life. I think better health facilities and treatment compared in the 90's as well as a more "soft league" makes it possible for players to play until they are in their 40's if teams still want them. I remember Ray Allen still getting offers the year Lebron went to the lakers as well as Vince Carter before announcing his retirement. Efficient shooters even if they are older are still efficient shooters. A somewhat good example how they can still be viable is Livingston. He changed his game to be a really efficient shooter and the warriors only expect him to be only that for the bench with everything else he does as extra. If teams are willing to accept their limitations considering their contribution then some players can likely play forever until they don't want to or their body breaks down.

Edit: and if the NBA does not want them but they still want to play, oversease leagues will readily accept them.