[zozbot234]

> All of a sudden the people in the south just suddenly decided to no longer be racist

That's pretty much what happened. The CRA (passed despite the opposition of southern Democrats) shifted the social equilibrium away from racism and a segregated society being totally normal and state-sanctioned, and Southern states had to reinvent themselves along different lines. They broadly chose economic freedom starting from the 1980s (despite continuing opposition by Dems, who to this day favor heavy-handed state intervention and a highly paternalistic attitude towards minorities), which is what created the modern Sunbelt.