Correcto-mundo!
The problem has been that every president hits the reset: (Mars-Yes; Mars-No/Low Earth orbit-Yes; LEO-No/Mars Yes; Both-Yes).
Every time the reset gets pushed, the design working its way to prototype->manufacturing gets cancelled; new specs get issued; new proposals submitted, evaluated, approved; new design gets underway, and BOOM->reset.
So, long story short, no follow on machinery ever gets deployed. Saves money, but the existing equipment degrades through use. The end result - nothing, but talk and videos.
No, in fact, that is not correct. The successor to the STS was in development, but a bit underfunded, and a bit behind schedule, so the anti-American Party of the Single Party State led by Zero himself deep-sixed it.
http://www.spacelaunchreport.com/sls0.html