Marlow
Champion
There are multiple theories. https://www.brookings.edu/research/an-analysis-of-out-of-wedlock-births-in-the-united-states/Expert theories aside, you still have not explained why the number of children born out of wedlock was significantly lower before the civil rights movement. According to the chart, the number was about 20%. Today it is assumed to be 65%.
"Efforts by social scientists to explain the rise in out-of-wedlock births have so far been unconvincing, though several theories have a wide popular following. One argument that appeals to conservatives is that of Charles Murray, who attributes the increase to overly generous federal welfare benefits. But as David Ellwood and Lawrence Summers have shown, welfare benefits could not have played a major role in the rise of out-of-wedlock births because benefits rose sharply in the 1960s and then fell in the 1970s and 1980s, when out-of-wedlock births rose most. A study by Robert Moffitt in 1992 also found that welfare benefits can account for only a small fraction of the rise in the out-of-wedlock birth ratio."