TL;DR: Achlioptas et al. as mentioned in this paper pointed out that composers who concentrate on choral music tend, oddly, to compose few instrumental pieces, suggesting, as it does, a narrowness of focus as well as technique.
Abstract: Thousands of choral octavos are published in the United States every year, almost all of which are gebrauchsmusik. There is choral music for children; for “swing choirs”; for churches—especially for the Evangelical mega-churches springing up like kudzu—for synagogues; and yet even more arrangements of Judy Garland’s greatest hits for gay men’s choruses. Although a surprising amount of this choral music is serviceable and competently crafted, most of these octavos are doomed to a quicker obsolescence than laptop computers. Pity the poor choral conductors who try to make sense of this profusion of new material and attempt to find repertory that is suitable for their ensembles. From the vast amount of choral flotsam and jetsam published annually, certain scores by a handful of fortunate composers rise to the surface and, miraculously, stay afloat, buoyed forward on a sea of consensus among conductors. Many of the commercially successful American scores are written by composers unknown outside of the insular world of the American Choral Directors Association. To those musicians and listeners not involved with choral music, the names of Clausen, Harris, Walker, and Spencer ring no bells of recognition. And, indeed, within the US musical academy, to be typecast as a “choral composer” is rarely considered a ringing endorsement, suggesting, as it does, a narrowness of focus as well as technique. (Those who deprecate composers who specialize in choral music might well recall that before the seventeenth century practically all composers—including, say, Dufay, Victoria, Tallis, and Palestrina—were of necessity “choral composers.”) Such denigrating imputations arise in part from modernist attitudes—still current within many university music departments—that exalt the abstract instrumental work over scores that use literature as a point of departure. And it is true that composers who concentrate on choral music tend, oddly, to compose few instrumental pieces. Some important composers who have created a substantial body of choral music have transcended such prejudices, however. One would hardly classify Conrad Susa, one of America’s most distinguished opera composers, as a “choral composer.” David Conte, a student of Nadia Boulanger, has written in a variety of genres, such as chamber music, instrumental music, and opera; choral music is only one important facet of the variegated catalogue of this prolific composer. Libby Larsen is another composer who works in a variety of genres, including symphonic music and opera. Morten Lauridsen—surely the most successful American composer of choral music since Randall Thompson—began to compose music for choruses only after serving a protracted apprenticeship writing lapidary songs and instrumental music. Eric Whitacre has sought to join the ranks of these distinguished creators, and has established, through untiring industry, a thriving career at a relatively young