Until the black shift is seen as absolutely unique, and one of a kind, then the answers to why cannot be found.
Ansel, my parents were born in 1930 and 1932. They lived through Jim Crow and the Great Depression. My dad's parents remained Republicans until the day they died (early 90s).
My mom's parents switched to the Democrats during the War Years, for many of the reasons that have been outlined. They saw FDR as a savior. They had suffered their whole lives, and the Great Depression made their lives nearly unbearable. It became very hard for most blacks of that era to refuse to give a Democrat their vote, when the Dems kept reminding them of all they'd done to save their bacon.
My dad's father was a very independent man who had professional skills, a can-do attitude a mile high, and a do-or-die spirit that would not quit. He was the type who would rather starve, than accept government 'charity'. He broke his neck and did whatever it took to keep my dad's family from ever having to go on "relief" (which was a horrible embarrassment to blacks of the day). He distrusted the Democrats, and saw the New Deal welfare programs for what they were...a trap.
Bottom line - black people succumbed to the temptation of free food and money, and sold their souls for it. What you might not know, is how long this process took. Even when I was a kid in the 50s, being on welfare had an enormous stigma attached to it, in the black community.