The traditional form 圓 is a meaning-and-sound character. 囗, an enclosing boundary, supports the idea of a complete shape, while 員 mainly supplies the historical sound. Simplified 圆 keeps the enclosure and uses the simplified inner form 员. The full character is later than oracle-bone writing, so this seal-form-inspired sketch emphasises a closed outer boundary around the sound component rather than inventing an ancient picture of a circle.
A piece of culture
Roundness and reunion 团圆 / 團圓 means “family reunion” or “being together again.” Round forms can suggest completeness: at Mid-Autumn Festival, families may gather under the full moon and share round mooncakes. Traditions differ from family to family, but the link between a full circle and togetherness makes 圆 / 圓 easy to remember.