Why is "African-American book publishers in the United States, 1960–80" trending?

Wikipedia Overview

While African-American book publishers have been active in the United States since the second decade of the 19th century, the 1960s and 1970s saw a proliferation of publishing activity, with the establishment of many new publishing houses, an increase in the number of titles published, and significant growth in the number of African-American bookstores. African-American commercial book publishers released a total of 154 titles in the period 1970–74, a dramatic rise from the previous high of 21 titles published during the five-year spans of 1935–39 and 1940–44. Institutional and religious publishers also increased their title output, rising from 51 titles in the years 1960–64 to 240 titles in 1970–74. Concomitantly, there was a widening in the scope of publishing objectives on the part of African-American book publishers, who began to release titles that not only advanced their particular ideologies but dealt with topics unrelated to Black Americana or Africana. Such diversity is emblematic of the increasingly important role in American culture and society of African-American book publishers.