What is a common reason for rubies being fashioned with shallow proportions?

Rubies are often cut with shallow proportions primarily because they are sourced from flat crystals. The natural crystal structure of rubies typically tends to yield stones that are flatter rather than more elongated or thick. To maximize the yield from these flat crystals while still achieving an attractive appearance, gemstone cutters will often utilize shallower cuts. This technique allows for more efficient use of the material while still retaining a visually appealing gem.

Considering the other options, while inclusions can affect the overall quality and cut choice, they do not specifically dictate the necessity for shallow proportions in the same way that the natural shape of the crystal does. Similarly, the polishing time for gemstones is typically influenced more by the type of cut and the overall design rather than the depth specifically. Lastly, while light reflection is an important factor in gem cutting, shallower proportions do not inherently result in increased light reflection; this is more related to the angles and facets of the cut. Therefore, the crystal structure is the most significant factor leading to the choice of shallow proportions in rubies.