I spent the better part of my teenage years eating raw carrots to be a better Ninja!
I don't know if they ever thought the myth would catch on as well as it did, but it's still widely believed today. (Perhaps because there's no downside, eating carrots is still good for you, it just doesn't improve your eyesight.)
Carrot cake also had a surge in popularity at the time (if the great show "Supersizers eat..." is to believed).