Sometimes there's a question here that should get a compact, detailed answer, and sometimes there's a question here that should get a panel discussion for a couple of hours. I'll try to help, though.

There has been a very long tradition of historians writing for the purpose of inspiring and educating people, especially the young. You find it in the Greek historians, like Thucydides, and the Roman ones, like Tacitus. And if you read some of the 19th. c. historians like Macaulay and Hippolyte Taine, the historian is very much present in the text, pointing out villains to be hissed, heroes to be cheered, saying when a Good Thing happened, or a Bad Thing. It's rather natural: we all have our own personal aspirations, and it's nice to have someone giving us plenty of examples of human endeavors that turned out well, or badly, so that we can succeed. And it's comforting to be told we're on the team that is doing well, making progress.

But this approach requires a lot of simplification, dividing everyone into heroes and villains isn't very correct, progress is a fuzzy concept...there are lots of problems here, the biggest of which is that it doesn't help us really understand why people did what they did, why things happened. I can say that Louis XIV revoking the Edict of Nates and going after all the Huguenots was a Good Thing, because then everyone had to have the same religion again. Or I can say it was a Bad Thing, because it was a cruel persecution of many innocent people. But neither explains Louis XIV, really; why he did it. Maybe the first guy to point out these problems was the German historian Leopold von Ranke, who famously said in one of his books, ""To history has been assigned the office of judging the past, of instructing the present for the benefit of future ages. To such high offices this work does not aspire: It wants only to show what actually happened". This notion of "source-based" history became very strong, in the 19th c., and it's what you will mostly encounter now. What we have noticed since Ranke, though, is that we all have our own biases, points of view. That's just something we have to admit, and deal with. It makes things complicated, and that complication can make a lot of history less satisfying to read.

But "writing to a purpose" is still very much being done. People will often post here asking about Howard Zinn, whose A People's History of the United States was written with the clear goal of showing it as a Manichean struggle of the poor and powerless against the merciless and powerful. And someone has written a Patriot's History of the United States in response to that, which minimizes all the injustice and makes everyone happy heroes. Both of these most would admit are pretty poor, biased, and source-negectful. But both tell a story a lot of people, a lot of customers, would like to hear. So, books like them are going to be around for a while.

Von Ranke, Leopold (1915) History of the Latin and Teutonic Nations