Mostly people would get or give the rabbits at Easter, thinking "oh it's just a rabbit" and little realizing how to take care of a rabbit (the information that most pet stores give, if any, is complete junk). Soon Peter Cottontail would be the size of a cat (rabbits aren't hamsters!), eating wires (you need to "rabbit proof" your home, because rabbits will chew on many, many things), or doing some other things that rabbits are meant to do, like sheding. So folks wouldn't want their pet anymore and dump their rabbits either on us or on a shelter, who would then call us. Actually, those were the lucky ones. The unlucky ones were "set free" in the wild (a house rabbit will do as well in the wild as a house cat, probably worse, because house rabbits don't always realize to run from things with teeth) or died of malnutrition from a diet of strictly carrots (they need hay for ruffage, leafy greens for vitamins, and dry rabbit food, although they like carrots and apples and all sorts of other things too).
Rabbits make wonderful pets, but not if you're going in blind.
Most time at the rescue was spent educating folks about house rabbits (I was amazed at how many phone calls with rabbit questions my friend would field each day) and adopting them out to good homes... with instructions this time