i know the reason and its neurological difference between people, lots of Americans(but especially Canadians) grew up with cartoons that had the one odd fetish here and there to sew seeds of furry, size, inflation, cest (looking at you, loud house) and many many more niche things.
my theory is the vore, unbirth fetishes and anal variation has roots in the fantastic voyage parodies that were popular in my time on top of the magic school bus.