Different design paradigms. In 1969, they had one shot to get everything right, and prepared accordingly (not to mention, they had a massive budget since the space race was all part of the cold war).
SpaceX is taking a different approach, fail fast and cheap. They are taking an iterative approach that allows them to learn from previous failures, rather than anticipating what all those failures could be and then over engineering the rocket to prevent that.
They are different approaches, and each has their own pros and cons. ¯\(ツ)/¯