Rayleigh says that Haki is nothing more than will, it is the spirit of the individual.
We saw Enma being presented as a cursed sword that extracts the Haki from the user and that only Oden managed to tame it.
Zoro has always possessed the Conqueror Haki, but he never knew how to use it, but then the question arises, how can the guy use it now?
Explanation:
Simple, as Enma extracts Haki from the user who is the spirit of the individual, she can extract CoC.
The Conqueror's Haki is also one of the elements that make up the individual's spirit, so this makes it possible to extract such a resource, Enma is extracting Zoro's spirit and for that she needs to "eat" more than normal, thus releasing her full potential .
The reason cursed swords are feared is because only those with great ambition can tame them.
Swordsmen without ambition are discarded by these swords and die.
Zoro has a strong spirit and therefore has a great affinity with these swords, the same applies to Oden.
Enma is probably a training tool for Zoro to learn CoC.