They were forced out. Biden’s South Carolina win was a cheat to strengthen his hand on Super Tuesday.
You are falling for spin. South Carolina was the first state with significant black voters. Black voters are important in the Democratic primary. Bernie and Pete could wi in states like Iowa and New Hampshire, where there weren't significant black voters, but they got clobbered in states with black voters.
Black voters rejected Bernie twice, and Pete once. Show me any evidence that black voters liked Bernie.