Just as the title says. Whenever I read a research paper on wireless power transfer via resonant inductive coupling the authors just mention frequencies that range in the kHz and Mhz range, but none of them explain why high frequencies must be used.
Low frequency resonant tuned circuits require high values of inductance and capacitance. High value and power efficient inductors cost money and are big thus, they don't easily find much use in resonant inductive coupling applications.
Added to this is that near field passive card readers read data from passive tags by the tag itself modulating the incoming magnetic field and, if that magnetic field is low frequency then the data rate that can be modulated is much lower. This would lead to slow data transaction time.