Skitters across the floor easily, is light enough to carry in their mouths, and throw around. Makes a funny noise on certain floors. It doesn’t have to look like something they would naturally hunt. Oddly, my cats don’t really like things that look like their prey. Their favorite toys are some plastic springs, ice cubes, and these feather teasers, but only once they have chewed all the feathers off and all that’s really left is the plastic body and a nub of feathers (they fly well, are easy to carry, and skitter across the floor well)
Short answer? Cats are weird little critters.