Because forcing out a huge amount of Haki is a special trait that we have only seen with Enma.
The user needs to have that Haki reserve, but Enma forces out more than he would without it.
At least that's the case until we see Zoro use Wado for example, and forces so much Haki into the blade that his whole arm withers the way it did with Enma.
The user needs to have that Haki reserve, but Enma forces out more than he would without it.
At least that's the case until we see Zoro use Wado for example, and forces so much Haki into the blade that his whole arm withers the way it did with Enma.