an opinion, Possibly the status of Missouri, Kentucky, Maryland, were part of the consideration in not pushing for the abolition of slavery. By late 1864, it was obvious, to most, that the South was going to lose the war. By that time it made no difference what those border states did, it would not effect the outcome of the war.
So taking a position on the basis of utility rather than on principle? Do you suppose that if Lincoln had informed the border states in 1861 of his intentions to push the 13th amendment, they would have remained in the Union?
It seems as if you are acknowledging that master manipulator Lincoln was just stringing them along until he could gain sufficient advantage that he no longer had to respect their wishes or interests.
If Lincoln had revealed this idea in 1861, the border states would have left too, and the South would have then definitely won the war. In fact, in all probability, with the remaining border states on their side, the Union would likely have been much less willing to initiate a war.