[Tallguy]

Because they destroyed the jigs and other tooling necessary, because nobody makes 1960s-vintage computer hardware anymore, because nobody writes code for 1960s hardware anymore (and they didn't save the source code), because the Saturn V was designed and built before environmental regulation ran amok...

If we still had the Saturn V hardware, it would be a possible to re-equip the system with new computers running modern code. If a B-52 can still fly after all these years there is no reason why a Saturn V could not also.

Your point about the Jigs, Tooling & Prints being destroyed is the real reason.

[BeHoldAPaleHorse]

"If we still had the Saturn V hardware, it would be a possible to re-equip the system with new computers running modern code. If a B-52 can still fly after all these years there is no reason why a Saturn V could not also."

Unlike the BUFF, the computers on the Saturn V are critical to safely flying the thing. Test-flying an expendable vehicle to make sure you coded it right is kind of pricey.