The Shuttle program didn't deliver on its expectations. It was supposed to be a cost efficient means to move cargo but it wasn't cheap or very good at it. Much of the transport was stuff just to sustain the needs of the astronauts.
What imminent demand is there for manned missions? When the first Shuttle went up they debated doing it unmanned. Just about everything is controlled from the ground anyway.
The shuttle program came through with far more than was expected. It was never to be a cheap transportation into orbit. It gave us the Space Station, the Hubbell telescope and is responsible for many things that we take for granted here on Earth. The ultimate explorer will be a man, not a robot.