There are many fruits where individual seeds grow in their own juicy little pods. Think about pomegranates, passionfruits, and raspberries.
There are many fruits where several of these seed-pods are wrapped up together in a single container. Think about apples, passionfruits, and groundcherries (or tomatillos).
Citrus fruits have been heavily bred by humans for a long time, and so they don't make a lot of sense as wild plants — because they're not.