Believe it or not, even the most gross photos of feet turns on people with a foot fetish.
The foot fetish is mostly a male subservient sexual fetish, in which emasculated men feel a desire to be degraded by having to suck on women's feet/toes.
Some psychologists hypothesize that this is a substitute for homoerotic displacement, wherein a male secretly desires to suck another man's penis, but due to the associated social stigma, instead focuses his sexual attention on female (or in some instances male) feet/toes, as a bony/rigid phallic (penis) substitute.
To answer your question, a person with a foot fetish is so consumed with the concept of being degraded, or sucking a penis (even though they may be too inhibited to actually do so), that they become abnormally obsessed instead with inserting toes or whole feet into their mouths as a substitute for normal human sexual relations, and any such depiction is the only thing which can sexually arouse them.
As barefootsies has acknowledged, he has had this compulsion/obsession for the better part of his life.
While he proudly talks about it, the fact is that the foot fetish is rooted in subjugation and shame, therefore barefootsies actually takes pleasure from his repeated public humiliation regarding his sexual disorder.
My advice to anyone that comes into contact with this sexual deviant is to wear shoes which cover your feet/toes entirely.
ADG