>>92921100>>92928527This and they have the 'underdog' thing going for them. Plus there is a lot of charm to see a world that would be insignificant to us, yet is everything to the characters. Something as simple as a mud puddle nearly killing a kid in Nimh is a great example, or how small animals in Mouseguard become terrifying beasts.
The idea got especially popular in the 70s, and moreson in the 80's with american tale, nimh, great mouse detective, and the rescuers.