[jessriedel]

DuskStar explained well why the Shuttle was not cost effective in terms of payload per launch cost. I want to mention that there was a tiny minority of missions where this isn't a fair comparison: where they were returning satellites from orbit to Earth. In those cases, the shuttle was not just deadweight that needed to pay for itself through reusability; it was a necessary part of returning the satellite.

This ability was used a grand total of just four times.

https://space.stackexchange.com/questions/15094/what-satelli...

It was not remotely worth making the rest of the launch system more expensive by an order of magnitude. Better to pay for a new satellite when they break, or (in the case of returning scientific samples) to design a sample-return function into the satellite.