Why did Biden win and Bernie lose?
One reason was the decline of caucuses:
Sanders was really hurt by March/April caucus states switching to higher turnout primaries. Change in the Sanders vote in each (W = he won anyway):— Dave Weigel (@daveweigel) April 13, 2020
CO: 59% -> 37% (W)
ME: 64% -> 33%
MN: 62% -> 30%
UT: 73% -> 36% (W)
ID: 78% -> 42%
WA: 78% -> 37%
AK: 80% -> 45%
Another was Biden's appeal to older voters. People over 40, who backed Biden, turn out in greater numbers than the younger voters who supported Sadners.
Brian Arbour at The Hill:
While Biden won his party’s nomination on the strength of his fellow senior citizens and with voters over the age of 50, Sanders was the clear winner among more than just college students , as many outlets reported.
My examination of voting patterns in this year’s Democratic primaries shows the real break between Sanders and Biden is not at college graduation, but at age 40.
Data from the Fox News Voter Analysis/AP Votecast of Super Tuesday found that Sanders finished first among voters between the ages of 30 and 39, with 43 percent of the vote. Among those in their 40s, Sanders only won 31 percent of the vote.
This pattern continued in the remaining contests that voted in March. Sanders won 60 percent of the votes among thirty-somethings in Arizona, but only 39 percent of those in their 40s; a 21 percent difference. There were similar large differences between the views of those ages 30 to 39 and those 40 to 49 in Missouri (59 percent to 38 percent), Illinois (54 percent to 35 percent) and Florida (45 percent to 24 percent). The numbers show those 40 and up were much less likely to vote for Sanders.