I also am not much of a fan of JMG's (seemingly?) nihilistic metaphysical views. I think at least part of it is motivated by the sort of knee-jerk anti-Christian reaction mentality this is quite commonplace throughout modern paganism. On the other hand, he might just be really cagey about his actual beliefs, as he's stated many times that he doesn't like making absolutist metaphysical statements, out of fear of his readers turning his ideas into dogmas. The fact that he favors The Cosmic Doctrine as his go-to cosmology tells me that he isn't in fact a believer in a nihilistic cosmos, as that doctrine is Monistic to the core and strongly resonates with Platonic/Pythagorean tradition.