You are completely misunderstanding the point, which is that that voters are operating in a media environment that is heavily skewed toward the corporate wing of the Party. The media controls the flow and type of information these voters are exposed to.
Further, key endorsements by figures like Jim Clyburn (at the behest of the Party, although he likely would have anyway) were absolutely instrumental in SC, as was borne out in the polling data.
There’s no ‘conspiracy’. It is not a secret that in many respects, corporate media (except Fox) functions as a mouthpiece for the establishment wing of the Democratic Party. They are very open about this.