Imagine that you were born and started off in life as a young person without any education about the past. Someone older than you might mention historical events, people, or trends, and you would feel out of the loop, like a very young child who misses whole portions of conversation.
You might even crave knowledge on this, wishing you could understand what is being discussed by the generation that lived through the actual events.
Consider that even before our formalized history schooling, people passed down information from generation to generation orally. Why would they do this?
Practical reasons include the need to understand how to survive and function in the world.
Our modern reasons go beyond this, but still relate to this desire to use the past accumulated knowledge and experience of human beings to better our own situation and prevent repeating mistakes made in the past.
Perhaps one of the most important reasons to study history is to spark interest to learn even more about these areas. It may seem as though history "happened" and now we learn about it, but our entire understanding of history changes over time. What we "knew" about World War II, for instance, changed when certain records were declassified and available to the public many years later.
We use different textbooks than we did 50 years ago or even 15 years ago. This is not simply because there is more to add to history textbooks as time passes, but also because historians gain a deeper understanding of the nature of past events and this makes its way into the way we teach these topics.
This can even be controversial! Who gets to write history lessons, and how does that influence what stories are told, and what stories are left out? Studying history well means we stay conscious of our own bias and the bias of those writing and teaching history.
Those who study history as professionals have this exciting task of examining the accepted assumptions about history and considering the evidence behind these ideas. Are they facts? Do we need more information? Where can we find that information so we can unlock more secrets of the past?
As another poster has said, one of the most significant reasons to learn history is simply to grasp our current state of affairs, and that of people all over the world. If we don't know anything about our history or that of other countries, we will have no clue of how to respond to conflicts, maintain relationships, or even plan for the future of our society in the most basic ways.