I'm pretty sure the problem with the shuttle was that it had too many (possibly conflicting) goals instead of one large goal.
It's manned, even though most launches probably could be done without crew. The deadly Challenger launch was risking human crew for something as mundane as launching two satellites into space.
Because it's manned, it has to be able to land at airports, because retrieving astronauts at sea is an unreasonable complication for launching a satellite. Damage to the wings will cause loss of the entire aircraft, something that is unlikely to happen to a capsule.
Because it is a horizontal landing system, the aerodynamics favor putting the shuttle on the same level as the external fuel tank, which exposes the wing to debris from the top of the external fuel tank. If you try building a vertical shuttle in KSP, you will notice that the wings give you too much control authority during launch. Fins are best placed near the bottom of the rocket.
It's reusable, which means wear and tear can secretly accumulate without you noticing. This significantly increases the design requirements for the critical components, like the SRB that had a poor "tang" design, which, as it turns out, was definitively not fit for reuse.