Because it doesn't make the slightest bit of sense. If you had a document from Lincoln saying he was abolishing slavery throughout the Union, and he was going to war against any state that didn't abolish it, then you would have proof that the war was about slavery.
Lincoln said the very opposite of that. He said he believed it was completely unlawful for him to do anything about slavery.
When Lincoln sent the men to invade the South, did he give them any orders regarding slavery? No he did not. What he told them to do was stop the "rebellion."
When did Slavery become a big official deal in the Union attacks against the South? About a year and a half after the war started.
Well the war can't be about something that wasn't an issue until a year and a half after it started, it has to be about something that was an issue at the very beginning of the war.
The question isn't why do "appologists" refuse to accept slavery, the rational question is why do people like you keep insisting that it was about slavery when you have absolutely no proof (like orders from Lincoln) that it was about slavery?
This is like saying "Border Security" is about Illegal alien children being separated from their parents.
No it isn't. Stop trying to dress it up as some emotionally satisfying justification that isn't accurate.
The war was about keeping control of the South and it's export money stream, and most importantly to make certain it didn't compete with the Northeastern wealth that was backing Lincoln.
"Slavery" is just a propaganda dodge to distract attention from the flow of money that led to the Civil War.
The motivation for the war being about slavery wa sin the south. It was part of their economic survival.
The south had fought to keep slavery since the declaration of independence and the articles of confederation and then the constitution. Since the 1820s they worried that more free states would be admitted than slave and after the Louisiana purchase that became very likely.
For you to say the south didn’t;’t want to keep slavery and that wasn’t a part of their motivation ignores there actions to protect slavery for over 75 years.
When the president and congress went to war, they may not have had slavery in mind, but they may. The northern members of congress wanted to admit more free states. Abolition was a big deal in the north east. But it doesn’t matter. By fighting the slave sates they were in fact fighting against slavery.
If that doesn’t make sense to you, I can’t help out any more..