Why is it important to learn about figures from the past who have been left out of history books?

Every semester in a history class, you are given a 500 page textbook. You don't like history since there's so many people to memorize, but you learn anyway. All the way back from when history started to the common times now, there had been so many people that lived during those ages. Some shined out more than others, which made it onto history books but there were still people worth noting that didn't make it in. While a man might've been less important than Thomas Jefferson, he could've created a cure for a deadly disease back then where he was miscredited or ignored due to lack of coverage. The sad truth is, history textbooks are limited. We cannot fit every influential people, and we focus on the most important but the ones not on the books may sometimes lead a stronger legacy than the ones mentioned in books.