Takes more energy to reach the orbital inclination of the ISS. Columbia is too heavy for the amount of thrust the Shuttle stack provides.
Got it. Thanks.
Many dont seem to understand that the Columbia is a glider, not a jet plane. It has some rocket pack for course correction but not for jetting around the neighborhood. In fact, the Shuttles have only one shot at landing. They cant turn around and try another approach to the runway. They are not powered. They are free falling from space.