It's everything. NASA doesn't have the money, brainpower, efficiency etc. to implement SpaceX development method. They can't fab it fast enough, nor can they iterate on the engineering fast enough, nor are they will to sustain the optics of a "government rocket blowing up" like Musk is. They don't have the caliber of engineering talent available or a workflow setup (high autonomy, long hours, better pay).
They don’t do the fabbing or (a lot of) the engineering now - they contract it all out. They could oversee those contracts differently but that would just be hiring SpaceX instead of Boeing or Blue Origin. Which they are doing some anyway.
