Answer:
Black Americans left the South due to a lot of conditions. after the South lost the war, there were still plenty of ways the South intentionally disadvantaged their black population. The biggest issue was the South's poor economic conditions, there was a lot of discrimination in the workplace which slowed the rate of class mobility growth.
Also, Jim Crow laws were common in the South, which upheld segregation and largely restrained the political and economic powers of Black Americans. Black people who migrated during the second phase of the Great migration were faced with racial discrimination, particularly restrictive covenants and reclining, which created segregated neighborhoods and therefore segregated schools.
Unfortunately when Black Americans arrived in big urban cities across the Midwest and northwest, tension began building in factories, largely by white workers. In the summer of 1919, the racial tensions became violent. In more than 3 dozen cities nationwide, white supremacists took over and created riots, massacres, and lynchings throughout the country. the violence that occurred during this period is dubbed "Red Summer" and at the time black americans were painted as violent, criminal, and marxists largely by popular news sources like The Wall Street Journal.