Inductive charging used for wireless charging often faces the hindrance of being too short ranged for many cases. There appear to be some workarounds such as using a capacitor to resonate them at the same resonant frequency. Please excuse the naiviety of the question, but when looking back at the humble solenoid, a simple iron core can drastically boost it's magnetic field strength. So, why not just stick an iron core into the middle of the inductive charging coils?
At the high frequencies implied by your question the eddy current heating of the iron core and the hysteresis loss due to the rapid oscillation of the magnetic field in the iron core will result in the Q-value of the circuit being very small.
In other words the energy losses of an iron cored inductor would be too high.
As long as the frequencies are not too high ferrite cores are used as they have a low electrical conductivity which means that eddy currents losses are small, low hysteresis loss (and a high magnetic permeability).
At higher frequencies no core is required and the losses due to air are very small.
So, why not just stick an iron core into the middle of the inductive charging coils?
From the energy and field strength perspective, at high frequencies, used in wireless charging, magnetic cores are not required and, at higher end frequencies, just would not work.
From the coupling perspective, cores would not be very effective, considering that wireless charging involves two coils residing in two different physical devices separated in space, i.e., they would not be able to share the same core.
For resonant charging, where high Q is essential, the losses associated with cores (if they could work at all at those frequencies) would be counterproductive.