Topic: What took NASA so long to reenter space?

Technicians have begun fueling the space shuttle Discovery for the program's first mission to space since the Columbia disaster two and a half years ago. The launch is set to go ahead later today after NASA fixed tiles damaged near the spacecraft's tail.

Why 2.5 years? How come it took so long for them to try again? It never took them this long to bounce back after the 1986 Chellenger missions. Or the Apollo missions. Why did it take them so long now? Is there a lack of rocket scientists? Lack of trained pilots for the Space Shuittle? What is the reason?

Please tell me your views.