people seem to have some inhibitions about using it
but i also believe it is because they fear getting mouth cooties!
mouth cooties are a disasterous and misfortunizing! oral transmission from belly button lint i gayruntee
common symptoms of this are "hey, this is not feet!" "grr, this is not feet!" "where are the feet", and last but not least, "wtf i want feet"
it could also be the sounds generated, and that's actually meant for cute situations, but nobody wants to be cutifying anything unless they're on 4chan which then they are pedophiles who enjoy cute
but even then there was an invasion of foot fetishists on 4chan and they are made fun of just like the rest of anybody who demands too much attention and catering when it's not our job to please their white slave-driving asses