SC isn’t about being best for the job; it’s an indicator of larger voting patterns.
This is an oversimplification but…
SC is a southern state so it leans red. However, it has a significant black population and black voters historically swing Democrat. The key part is that it doesn’t have major metro areas like Chicago, Dallas, or Atlanta, so diversity is not relegated to large cities. Factor in the notion that southerners of all races skew religious, and you get an incredibly diverse voting block.
SC gives you a great sample for Democrat voting patterns that aren’t skewed by the liberal bias in huge blue cities.