You overlook the fact that for compensated emancipation to work it required an interest on the part of Southerners to allow emancipation, compensated or otherwise. Such an interest did not exist.
Also an interest on the part of poor southerners and all northerners in being taxed (a lot) to pay for compensation to rich southerners. Nobody wanted it.
But you are quite right. It took till February of 65 for the CSA Congress to recognize they might have to recruit some slave soldiers and free them after the war. Anybody who hadn’t figured out the necessity some time before that needed a really big cluestick.
But even they weren’t as dumb as the slaveowners of KY, who were offered compensation but instead insisted on keeping their slaves only to lose them by the 13th.
Seriously, by 1864 who couldn’t see that slavery was going doowwwn? Only someone who was obsessive and irrational.