I find people usually like a specific amount, and that often there is such a thing as excess, even with desirable things, traits. This also changes over time, and from culture to culture. Another example is the coloring of clothes. In ye olde times, a vibrantly bright colored article is a rarity, because dying it, and then keeping it clean are not trivial tasks. Nowadays, bright basic colors such as royal blue can easily seem cheap, like something from a bazaar. And many subtle tones, such as colors resembling what you'd find in nature, are popular.

Shininess is one property people appreciate in gems, but not the only one. Many so-called fine things are loved exactly because their quality can’t be pinned down on a simple scale, but rather is a blend of subjective evaluations whose weightings are constantly evolving as tastes change.

Is the best wine the one with the highest alcohol content? The best chocolate the one with the most cocoa or the most sugar? The best painting the one with the most contrast? Etc.

When moissanite sparkles, it sparkles with rainbows. Diamonds sparkle with just white light.

They are very similar, and you need to look very closely to observe the difference.

One of the nice things about moissanite is it allows creating jewelry that otherwise is economically unaffordable with diamonds.