ISTR it was made a condition of shuttle funding that the Saturn V blueprints were destroyed, to ensure NASA were unable to go back in future to ask for them to do something else. Yes, a decision made by politicos based purely on funding.
Similarly the shuttle's principle design flaws were brought about by congressional funding decisions. The original design was intended to be launched from an aeroplane instead of the tank and booster stack but this was stopped when Congress saw an alternative concept with lower R&D costs even at the price of much higher per launch costs. This was a decision motivated by funding which directly led to both shuttle accidents.
Similarly the other weak link - the heat shield. Congress thought they could get away with a single design for both heavy lift and manned launches. This made the shuttle far bigger and heavier than it would have been and by necessity makes reentry a far longer process. A heatshield that has to survive 10-15 minutes reentry as is the case for the shuttle is far more challenging than one lasting 2-3 minutes as was true for Apollo. This led to a complex and fragile design which in turn led to the Columbia accident. Again, a poor decision motivated by funding rather than engineering.