The nice thing about rockets is that you can start as small as you'd like and build progressively larger and larger rockets and get the engineering details right before you have to worry about getting into space.

Space elevators, skyhooks, and launch loops are all big enough that it's an all-or-nothing deal. You can test individual components, but a whole end-to-end space elevator has to be exactly the distance between ground and geosync or else it just doesn't work. At best, you could build smaller versions of this stuff on the moon first and then scale up to Earth-size later, taking into account such factors as water, atmosphere, and the fact that the Earth is not tidally locked with the sun. But that requires hauling metric fucktons of parts and equipment to the moon, even if you're using lunar resources to build the space elevator itself, so there's no guarantee you end up ahead in the end.

The basic physics behind rockets is simple as all hell, and it still required von Braun to spend his entire adult life building progressively bigger and bigger rockets and refining the design details. The V2 only needed to be able to land nose-first 200 miles from where it was launched, but without that knowledge and experience, the Saturn V would have been impossible. That's the kind of iteration that's fundamentally impossible with these other launch systems.