your data is not quite correct.

Up to March 10, Biden earned 723 delegates to Bernie's 635.

vote percentages were close at 31.8% to 29.8%

Biden had 11 first place results and five second place.

Bernie had 7 first place results and 12 seconds

Biden simply pulled away after April 10th. I do not consider it "organizing" so much as self-sorting. Other than Elizabeth Warren, all the rest of the candidates in the primary were more like Biden than Bernie- and it's natural that citizens who preferred them would gravitate toward a like candidate

https://en.wikipedia.org/wiki/Results_of_the_2020_Democratic_Party_presidential_primaries