The bar is set pretty high for a lot of these athletes in Olympic sports. This is really their only time to shine in the spotlight. Even big sports fans don't follow these sports outside of the Olympics. If you want to be a household name star in track (or swimming, or gymnastics, or volleyball, etc.) the only way to get there is to win at the Olympics.
Isn't Jordan Wieber the defending world champion for gymnastics? Doesn't matter, nobody cares. Gabby took the prize at the Olympics when the world was watching, so she will be the one signing the endorsement deals, smiling on the front of a cereal box, and landing a spot on Dancing with the Stars.
If you want fame and fortune without coming through on the biggest stage, grab a basketball or a football.