I think that foot fetish being the largest is iffy. I think it's the most well known and has gotten more acceptable as models on OF and such are down with indulging a fetish as non-invasive as feet. I mean, I doubt they're complaining about having to get another pedicure at a high end day spa that is being paid for by some rich guy in exchange for exclusive pictures. It's also easy to promote on social media as none of them are banning pictures of feet compared to getting a community guidelines strike for just showing a bit of cleavage.

You think feet clock in higher than bondage, leather, lingerie... I'd be super into seeing some figures, because that doesn't mesh with my intuitions at all.

I'd also like to offer a counterpoint to the hypothesis that the commonality is the creep factor, and suggest that it is, rather, the social disapproval that leads to that. Why? For one thing, that disapproval makes it harder to satisfy. Sex is a need for humans in a similar way if not as intense as food, and people will display behavior amoral at best and immoral at worst in service to that need. Obligate foot fetishists, who can't get off without it, have therefore a more limited window for satisfaction of that need, whereas people who have options can get off other ways and don't have the heavy breathing and sweating aesthetic about them in the same way.

I honestly believe a large portion of the feet fetish guys are into it because it's weird and makes them an outsider, and less because they actually find feet appealing. I also kind of feel like it's a 4chan thing where enough people pretending to be into something eventually convinces others into just actually being into the thing. Anyhow, feet are fucking gross, thanks for coming to my talk!