The point is that these "desirable" attributes were chosen by the diamond industry to promote their own gems. Why is "fire" or "brilliance" the reference by which gemstones are judged by? This mindset is exactly what the diamond industry has created, and the irony is that the author has taken the same sheepish following that diamond customers have.
Probably because those criteria actually look good for jewellery.
Which makes sense, easier to get someone to pay more for a gem they think looks good, than to make them pay more for a gem they don't think looks good.
