I wonder the same thing, but I think the anger had been building since the 1830's, and the South was just ready to try something different.
Anger at what? The Slave Power got just about every thing they wanted during those 30 years. They controlled both houses of congress. They controlled the White House for all but 4 years. They controlled the Supreme court with a majority of pro-slavery southerners for all of those years. They got all the legislation they asked for from the Missouri compromise through the Fugitive Slave Act, the Kansas Nebraska Act and the Dred Scott decision that overturned not only the Missouri compromise but also the Northwest Ordinance, and the only concession they made during that time was to agree to closing the Slave Pens and Auctions within the City of Washington (actually in the shadow of the Capital building itself.)
I agree there was anger, but it was not anger based on anything that the Federal Government or the Northern States had done to them. It was a manufactured anger at even being criticized for their "peculiar institution". It was not enough for them that most of the people of the North simply turned a blind-eye at slavery. What they were demanding was that all people agree with them that slavery was a positive good and for the people of the North to follow their lead and forbid criticism of slavery in any way.