We do not know. It is not known just how or where the 'laws of physics' are ultimately proscribed for our universe. One possibility is that there is/are/ were an infinite number of alternate ways that our universe could have emerged from this quantum process. In some sense, all of these alternate versions were/are realized, and that our universe is one of a large number that were imparted with the right laws to continue the Big Bang and the evolution of our universe. Of course we do not know why there even are natural laws in the first place, but we do know that increasing temperature and energy can seriously alter the way these natural laws behave, and also the properties of the particles that they interact with. The natural laws at the 'beginning' of the Big Bang may not have looked anything like the ones we now see, if you believe the hints that seem to be coming from high energy physics experiments. Some physicists in the last 10 years have speculated that at sufficiently high energies, all is complete chaos, and that natural laws emerge from this the way that ice emerges from water cooled low enough.
The vacuum fluctuation served to bring into existence the spacetime 'stage' and populate it with raw energy in the form of a small number of fundamental fields, perhaps even gravity as the MOST fundamental field. All else may have emerged...almost miraculously...as this quantum system cooled and found itself by chance trapped into one path of evolution favoring universes like ours as the outcome. The same system, however, could have evolved along other paths to produce a very different universes.