As someone who has done research on why I have an attraction to feet, there is a current theory in the bio-psychological spheres of research that explains that the somatosensory cortex (the area of your brain responsible for processing sensory input as good, bad, or neutral and then relaying that information to the cerebral cortex so that decisions can be made based on said input) is right next to the area of the brain that controls feet and toes. This can lead to a crossing of neurosensory input in which the somatosensory cortex, which processes stimulation from genitalia, associates that arousal from stimulation with the feet and toes. That isn’t always the case for how foot fetishes develop, but it is a common explanation. Do with that what you will