Because, again, it's such a minor thing you barely notice it throughout even Fallout 1. Just explain it with tech, that's the better scifi way. Psionics is just Magic being shoved under a scientific paper. It didn't reappear in Fallout 2 or 3 to my knowledge and the Forecaster in NV was thankfully some kid I never had to speak to ever again. Why keep wasting time and code on such a small, ill-fitting thing?