The tone control is basically a Low Pass filter meaning it only passes frequencies lower than the highest frequency allowed by the combination of resistance (the pot) and capacitance in the circuit. I forget the math but the higher the resistance, the higher the frequencies that will pass.
It is like raising the height of a doorway so taller people don't have to duck. Fortunately, I am short so I don't have to worry about hitting my head when I walk through a door.
If this information is redundant, my apologies.