why is eliza drawn from life

The author herself says that Eliza's character was drawn from life. Stowe based Eliza's character on a quadroon girl she saw on the steps of a church while traveling through Kentucky. She was shocked when she found out the girl was a slave. Although, Eliza was patterned after this girl Stowe had never seen before, other slave girls she'd known through the years added to Eliza's story. She was drawn from life..... many lives.

When people write novels, they often base their characters on someone they know. This is not uncommon; in order to provide universality, one must describe characters who are relatable to the reader.