If man-made diamonds have the same properties as real diamonds, why do you think they are less expensive?

Because they're made by man within a certain period of time.

Explanation:

Real diamonds are not rare as is, it's the picture that has been imprinted into all of our minds that gives them worth. Real diamonds take a long time to make, sure, but they're not rare. Compared to man-made diamonds real diamonds are hard to come by.

payments were made after the 1940s.

in the 1980s, a commission held investigations and made recommendations.