Eh, they're culture and history. On a global scale we have the ruins of Greece and Rome; on a local scale, people put up monuments to help remember local heroes (or to help memorialize local tragedies).
Culture and history are guides to behavior. Without culture & history, we drown in possibility and freedom. Without culture & history, one direction is as good as another, and so is staying in place. In other words, without culture and history there is no reason to do anything. If there is no difference between up or down or sideways, then why move at all?
So it's good to have history and culture to provide some examples and guidelines. Whether it's Martin Luther King or John Brown's raid on Harpers Ferry, or some Revolutionary War general, it's interesting to see how ordinary citizens stood up for a cause and became examples of what to do (or what not to do) in times of crisis. Some local pimply-faced kid got promoted to a position of responsibility, and then somehow ended up under fire; we're interested in how he or she fared and how many lives were saved or lost as a result.
One of my favorite authors is Robert Greene. He wrote "The 48 Laws of Power," "The 33 Strategies of War," "The Art of Seduction," "Mastery," etc. He's an historian, with a degree in classical studies. He can tell you exactly who all the great figures of history were, and what made them great or evil or fascinating or successful or a failure, etc. What was the appeal of the Kennedy brothers? Andy Warhol? Cleopatra? Alexander the Great? Marilyn Monroe? Che Guevara? Sun Tzu? Mata Hari? The great artists of history? The great dictators and rulers of history?
Of course, history and culture shouldn't be elevated to the point that they turn into a religion or a straitjacket. I'm into a little fashionable anarchy when culture turns into tyranny or authoritarianism; I'm into the trashing of historical icons when history is used to punish nonconformists.
But to learn about history and the great names of culture is to learn about humankind and what moves us. And local monuments are part of that cultural legacy. Maybe they are only local history, maybe it's just someone memorialized by a name on a school or on a highway, but presumably they are important at least to the people in that particular region.