Bernie Sanders had the states with a caucus on his side. New people showing up. People who were not regular or loyal Democrats.
because facts matter - quotes:
By this measure, Clinton was quite dominant. She trailed Sanders in pledged delegates only once, after Sanders won New Hampshire early on. But she
regained the pledged delegate lead after Nevada and never looked back. After Super Tuesday on March 1, Clinton had a lead of 191 pledged delegates, and it never dropped below 187 pledged delegates the rest of the way:
Hillary Clinton will officially become the Democratic nominee for president this week, at which point we’ll finally close the chapter on the 2016 primaries. But…
fivethirtyeight.com