The hysteresis loss is proportional to the frequency. The hysteresis loss should increase with an increase in the frequency, however the hysteresis loss remains almost unchanged. The reason is that the flux density in the core gets decrease in the same proportion of the increased frequency.
The eddy current loss is proportional to the square of the flux density and frequency. With an increase in the frequency the eddy current remains unchanged because the product of B2m f2 remains unchanged as flux is proportional to ratio of V/f.