Why are rockets so hard to make today? (Score 1)

In the 1960s there was a huge push to put a man on the moon. Countless hours and dollars were pored into the program, resulting in several rockets, including the Saturn V. I would assume the plans for these rockets still exist, and could be used today to build new rockets to put people into orbit, the moon, and beyond.

Why, then, is SpaceX working so hard to develop and test new rockets? Were they starting from ground zero, or were they able to access Saturn V specs and plans? We had rockets that got us off the planet before - if we threw enough money at it couldn't we just build new Saturn Vs?