User blog comment:B214/Shin DxD 1 discussion/@comment-32252462-20181203135619/@comment-2404:440C:105C:6600:D88A:6FF4:D040:83EA-20181204232841

Because the only known way to create clones of dragons in the story so far is through the holy grail which heaven doesn't currently have. I imagine creating an artificial human is a whole lot easier than cloning a legendary dragon