I don't think it has anything to do with Diana becoming a goddess, I think it has to do with the capabilities of Diana that has rivalled the capabilities of gods or goddesses. The feats that she can perform are on a god-like level, and she has been consistently portrayed this way for decades, not just by Byrnes but by several creators. The word god and goddess (with a common g) have been thrown around to describe several characters in the DCU who are able to do things which far surpasses the skills and aptitudes of ordinary human beings; it doesn't mean that people pray to them, and it doesn't mean that they are ominpotent or ominpresent as the Almighty. It just means that their strength, speed, and other abilities are in a much higher category than that of regular people.
I highly doubt that people in the DCEU have been praying to Diana for the past 100 years.