Here is my thinking on the Bernie vs other vote in the 2020 Democratic primaries.

Bernie was a familiar figure from the prior run for president against Hilary Clinton, and started running early. There was no other clear candidate for those who did not have confidence in Bernie Sanders. Not for his goals, but for his unrealistic approach for actually achieving them (as mirrored by his supporters). Also, Bernie’s lack of support for Democratic candidates, and lack of achievements (no surprise given said unrealistic approach to national politics). The people of color in South Carolina tipped the scales to one non-Bernie candidate, and that was all she wrote for Bernie Sanders.