Hugh,
the quick answer would be - because of my personal taste.
The somewhat longer one - I doubt, somebody interested primarily in Bali, how it was before 1908, when the order changed, would like this kind of ivory crosspiece carving.
If somebody, who has visited Bali in recent times, would have chance to visit Bali around 1900, he most probably would be astonished, how much of "traditional" Bali is missing - music, dances, stone and wood carvings. All of this did exist back in this time of course, yet in a completely different style and with completely different expression.
On the other hand, this style of crosspiece carving is a genuine part of Balinese art of, let's say, 1950 - 1965, as such it is completely acceptable and genuine. It is kind of "aristocratic" version of the dancer's Keris.
http://www.vikingsword.com/vb/showth...ht=dance+keris
For anybody interested in changes of Balinese society and art during the XX century, I recommend the book by Hildred Geertz, "The Life of a Balinese Temple. Artistry, Imagination, and history in a Peasant Village".