At that level of talent and accomplishment, there is always the chance that a non-prospect is one "aha!" moment of understanding away from turning that corner, and becoming good enough. A coach says something, or an opposing player does something, or the player himself looks at something a different way - and suddenly one particular kind of breaking pitch in the dirt is readable, or whatever. Odds are against, but since the player doesn't know what he doesn't know, necessarily, the hope is there, and if you love the game anyway, you hang on for another year.