You've twice referred to blacks moving to the cities from the suburbs, but the movement from the south to the northern cities was from rural areas. The suburbs were populated by people wanting to escape the cities, mostly because of urban decay, racial biases and expanding incomes. Blacks have never had a high percentage of the population in (especially northern) suburban areas. Whites are the dominant racial group in all non-rural areas with low population densities; surprisingly, Asians have the highest concentration in urban areas.
The south to north migration of Blacks was, and still is, popularly blamed on wide spread racism in the south. The reality is a little more complicated, but the racism in the south during that time period was considerably worse than what they encountered in the north(which wasn't all rainbows, flowers, and unicorns either. It just happened to be an improvement over the south). What the bigger driver of that was that the north continued to industrialize after the Civil War, and further, they urbanized much more rapidly than the mostly agrarian south did, even after reconstruction. The urbanization of the south, outside of a handful of cities(almost literally!) has largely been a phenomenon of the late 20th century/early 21st century. Industrial need for workers in the north, paired with the ready supply of labor in the south that was practically being run out of their home states, morphed into that migration.
Another thing in the mix, which also skews numbers is the advent of the Pullman Cars, which often played to a sterotype(and took advantage of the lower wages they could get away with paying blacks), results in a large redistribution of blacks across the country(which is how that follow-on migration to the north actually started, IIRC; some blacks went to work for the railroad, were relocated to the north, found out there was all kinds of work available up there, and wrote home about it...).
But sticking with the railroad/Pullman Car workers(again, the workers in the Pullman Car's being an overwhelming majority black), this resulted in Black communities cropping up in practically every significant Railroad town in the United States, and those communities existed so long as the Railroad remained the king of transportation.
Once you get into the 1950's, and in particular the 1960's, the railroads start bailing on passenger transportation as the Automobile and Air Travel starts killing their market. The Pullman Cars, as a consequence, get pulled out of service, those (again, overwhelming majority Black) workers are then without work, and have a skill set that probably isn't in high demand in most of those small to medium sized(rural) railroad towns, which may also have been hurting from the railroad cutbacks themselves. So they move to somewhere that they can find work at, and collectively, this resulted in many railroad towns going from having substantial Black populations to having a virtually non-existent Black population just a couple decades later(and getting "reputations" as well).
