They must have been the most commercially successful bits of toxic positivity merch I've ever known. Back when they were a thing, your chances of getting in a road-rage based auto accident spiked each time one of these was on the back of a vehicle in motion:
Show
They seemingly vanished off the face of the Earth, and good riddance.
Taken subjectively, yes, I can definitely see the appeal.
Growing up with (younger at the time) adult
road raging with smiley stickers on their cars and "don't worry, be happy" being said as a thought terminating cliche gave me a different experience back in the 80s.