It's not really a "Moore's law" thing at all - it's more that, like every single other technology in history that isn't specifically semiconductors, batteries don't follow an exponential improvement curve. They also evolve slower than many other technologies even on a more typical growth trajectory, because battery chemistry has way less room for easy improvement. There's only a few battery chemistries that could even theoretically offer much better density than lithium-ion, and we've been trying to make them work for a long time.