I have loved history since I was six and my parents got me my first adult history book. I love how all stories fit together, understanding why things happened the way they did, how and why people in the past thought differently than we do today, all of it. If you read a textbook, though, history is just memorizing one thing happening after another.
Part of that might be my (American) education system's fear of controversy: explaining what motivated abolitionists and slave-holders in the 1850, the actual stakes over which they were fighting, would not be popular in many states, and some parents would no doubt object. But also, it's complicated because the past is a different country- all of a sudden you are having to explain the way that the economics of the Industrial Revolution changed the demand for complimentary goods (1), the Curse of Ham (2), the way that printing presses functioned in antebellum American democracy (3), and the pre-Civil Service patronage system (4). Basically, you have to teach a college level course to understand how things were different then and why they happened. And really good teachers can simplify the details down to an age-appropriate level, but most teachers are, well, average, and so memorization is a lot easier path to follow.
1: The beginning of the industrial revolution mechanized looms and spinning wheels, and mechanized cleaning raw cotton. As basic microeconomics suggests, those improvements suddenly massively increased the demand for cotton. Those demand spikes transformed large slave owners from people who understood that slavery was bad and wanted to see it ended but not quite yet to people who thought that slavery was a positive boon for the enslaved people they owned. You can actually see this in their writing, in 1800 most slave-owners think that slavery is on its way out and will not spread much, and in 1830 slavery is the best thing that God gave people anywhere.
2: The Southern Baptist Convention created itself in 1845 because so many didn't think that National Baptists in the General Missionary Convention were committed to defending slavery and the Curse of Ham, and they wanted to be part of a religion dedicated to the idea that White people should rule over Black people.
3: Before the secret ballot each party would provide its own ballots, pre-marked, and you just turned in the ballot of the party you supported. This naturally meant that each party had its own printing press in each town, which meant that they also had newspapers, pamphlets, and the like, and the press-owner was almost always one of the most committed political partisans in an area. Then when their party won they would get the contract for printing all documents the government needed in that area. This is a major driver for political polarization in the 1840's and 1850s.
4: Before the existence of Civil Service protections, basically all of the staff of the government would change over with a new Administration, every postmaster in every town would be appointed by the President and would change with every election. The fear that a Northern President committed to abolition would use this patronage- and printing contracts to printing press owners- to build a large segment of white southerners committed to abolition- who would in turn spark a slave revolt- that was why so many Southern states tried to leave the Union at the election of the first Republican President, before he was even inaugurated or had a chance to do anything. Because if they waited, he would appoint abolitionists to every town in the country, so they had to get ahead of him.