Southern Democrats voted Democrat because they could never vote for the party of Lincoln. Simple as that. This changed in the 1960’s.
Agreed, and it's also fact that Democrats like New York Governor, then President Grover Cleveland (served twice during 1885 to 1895), were genuinely conservative.
No dispute about that.
But the "progressive era" infected both parties, and Democrats (Wilson, FDR) far more enthusiastically than Republicans like Harding and Coolidge.
Regardless, the Solid South solidly supported Democrats even into the 1950s and liberal Democrat Illinois Governor Adlai Stevenson's run for president against Dwight Eisenhower.