That is because the Ordinances declared what they were doing while the Declarations spelled out why they were doing what they were doing.
That’s because to the seceding states, slavery was a constitutionally protected institution, not an issue at all if only the Federal Union would honor it’s compact to the states and it’s sacred oath to the constitution.
But the federal union did honor its compact insofar as slavery was concerned. It wasn't until after the southern states rebelled and committed acts of insurrection against their fellow states did the union react.
Such an assertion proceeds from a false premise. The secessionist states were acting constitutionally, not rebelliously. Consequently, there could be no insurrection on their part, only acts of self-defense.
It was northern aggression directed by the Federal Union in the person of Lincoln that acted to crush the secessionist states for seceding, something the states had every right to do. Lincoln by force of arms would compel the states to rejoin the Union, or they would be destroyed. There can be no doubt that the Federal Union broke the compact. The secessionist states wanted only to leave the Union in peace and go their own way, independent, sovereign, and free. As was their right.
The original Constitution as agreed to by the several states specifically enumerates the powers granted to the Union government and explicitly states that all powers not granted to the Union government are reserved to the states, or the people. Since the authority to remove a state from the Union is not granted to the government, (i.e. Congress can't remove Virginia) the authority is reserved to the states.
The 10th amendment was never more clear or pertinent. The ultimate authority of deciding if a state is to stay with or vacate the Union was not granted to the Union, thus it resided solely with the states.
That's it, that's all it ever was. Lincoln could not have cared less. He couldn't wait to violate the compact and ignore his oath of office. So he didn't.