20th century composers who were accused of being "sell-outs" to the public's musical tastes by modernist composers are referred to as

20th century composers who were accused of being "sellouts" to the public's musical tastes by modernist composers are referred to as betrayers. The term 'sellout' was introduced in America approximately between the late 1950s and early 1960s, meaning that a composer, or an art/social activist preferred commercial success to the pure form of his activity. Also, if you look through the classic dictionary of English, you will find the examples of how the verb "to sell" to functions as “to betray”.