Why not?
Well firstly, it makes you look greedy, and people don't want to admit they are doing something unprincipled because they are greedy.
Secondly, making the North aware of how much money they would be losing would galvanize them to oppose your efforts. By keeping the focus on "slavery", you remind them of how much they don't want you. Telling them you are going to take control of about 700 million per year that was currently being controlled by powerful men in the North, will make them start worrying about their own money, and nothing gets a man ready to fight faster than being told you are going to take some of his income away from him.
Just as "slavery" was a smoke screen for why Lincoln wanted to invade the South, so to was it a smokescreen to disguise the monetary reasons why they wanted out.
That it was always about money becomes clear when you take into account the secession crises of 1828, which no one can deny was just about money. There was no "slavery" issue clouding up people's understanding of each other's motives during the previous secession effort.
There are several problems with your argument here, including:
1859: 94% of US tariff revenues came from
Northern & Western ports, only 6% from Southern ports.
DiogenesLamp: "Just as "slavery" was a smoke screen for why Lincoln wanted to invade the South, so to was it a smokescreen to disguise the monetary reasons why they wanted out."
Pres. Lincoln did not "invade the South" in 1861 to "free the slaves" -- that was not his stated goal then -- even though seizing Confederate's "Contraband of War" was very much part of Union tactics from almost Day One.
Lincoln's main goal then, and throughout the war, was restoring the Union.
Confiscations (1861), emancipation (1862), abolition (1864), citizenship (1868) & voting rights (1869) for freed slaves were consequences of Lincoln's main focus, restoring the Union.
DiogenesLamp: "That it was always about money becomes clear when you take into account the secession crises of 1828, which no one can deny was just about money.
There was no "slavery" issue clouding up people's understanding of each other's motives during the previous secession effort."
What the 1828 - 1830s "Tariff of Abominations" Nullification Crisis proved was that no reasonable Southerner was willing to declare secession and war on the United States only over tariffs.
Even when, in 1830, tariffs rose to nearly four-times higher than 1860's 15%, only few of the South's most globalist elites were willing to commit treason and rebellion against Pres. Andrew Jackson.
That's why the 1830 Nullification Crisis ended relatively quickly and bloodlessly.
What did motivate a majority of Southerners was slavery, and by 1850 many Southerners ("Fire Eaters") were calling for secession over slavery issues -- issues which were then resolved (at least temporarily) by the Compromise of 1850.
But what was resolved in 1850 became unresolved again by the late 1850s, especially as a result of the 1857 SCOTUS Dred Scot ruling, 1854-1859 "Bleeding Kansas", John Brown's 1859 raid, and from 1856 on, threats from "Black Republicans" with their 1860 leader, "Ape Lincoln".
All of that was about slavery, not tariffs.