Glib Answer:

Probably because historians are really good at pointing out how things people like are actually bad and telling unpleasant truths.

Less-Glib Answer:

People do pay attention to "the past"; in fact, people use historical claims to cement and validate most of their core beliefs. Ask two people on opposite sides of any political spectrum the basis of their beliefs in the U.S. and chances are they will both cite the "Founding Fathers" [ugh, there were other people besides white men there] and historic documents like the Constitution and the Declaration of Independence. Nazi, KKK, and white supremacy ideologies are all deeply rooted in ideas about the past.

The reason people don't read history is because they think they know it already -- or know it well enough to support the claims they want to make. The reason people dislike historians is because historians call attention to the inaccuracies, fallacies, distortions, and just plain fabrication that constitutes a lot of people's understanding of history. Since people use history (sometimes without seeming to realize it) to narrativize, contextualize and lend meaning to their lives, revisions to what they thought history was is often experienced as a personal attack.

Nor am I talking about individuals and individual understandings -- many historians have studied the phenomenon of popular/collective memory in the past. For a very brief case study that also explains the historian's craft much better than Ken Burns ever will [pardon my snark], might I recommend Alfred Fabian Young, The Shoemaker and the Tea Party: Memory and the American Revolution (Boston, Mass.: Beacon Press, 1999).

In this book (almost 20 years old at this point!) Young embarks on a biography of sorts of the man who coined the phrase "Tea Party" to describe the event with the dumping of British tea into the Boston Harbor preceding the U.S. Revolution. The man, George Robert Twelves Hewes, was a participant in this event and many others, and coined the phrase in his memoirs. An excerpt from the intro:

As I worked my way through Hewes' remembering, I realized that my subject was not only his experiences, what he had done and thought during the Revolution, but the way he remembered them [...] To make sense of his remembering, I had to peel his biographers away from him, unravel his memory from his exeriences, and then intertwine them anew, analyzing why he was remembering the way he did. In other words, his memory itself became my subject. [...]

More than names are at stake in what and when they called it the Tea Party. The contest over names, I discovered, is part of a larger contest for the public memory of the Revolution, a process I now think of as a willful forgetting and a purposeful remembering of American history. What does it mean for an event to be 'lost' and then 'found' and given a new name? What does it mean for a person to be plucked from obscurity, made into a celebrity, and then more or less forgotten?