I have a Gen Zer who never, ever wears sandals. She has never mentioned the foot fetish thing, but I think it is more what they perceive as socially acceptable within their groups and fashionable.
But the fetish thing strikes me as a really bad reason not to wear sandals. Realistically, while they may not be as popular or as exploited online, there are people with ring fetishes, earring fetishes, muscle (usually on women) fetishes, even disability and ethnic background fetishes. Honestly, you name it, and there is probably someone who has a fetish for it. You cannot live your life always worrying about the creeps who might take your picture in public.