There's also a steep difference in the tolerances you can permit. A rocket -- especially one with any hope of reusability -- is something that can't be built without getting very very close to the maximum tolerances possible within the bounds of physics. Look at the temperature differentials in a rocket engine for example... it involves nearly instantaneous transitions from deep cryptogenic temperatures to ones far beyond the melting point of any known material that can only be sustained with constant active cooling. The fact that we can achieve any level of reliability with a device this insane is really a testament to human ingenuity, but it doesn't give you much margin for error. Screw up just a tiny bit and the rocket is going to do what the laws of thermodynamics really want it to do: explode in every direction instead of just downward.

An airliner, even a supersonic one, is more forgiving. Over-engineering goes a long way toward adding nines to your reliability. We've been doing supersonic flight with reusable craft since the 1950s, and there aren't a whole lot of unknowns remaining. That means it's mostly a manufacturing and operations optimization problem.