Context for Minnesota's results
Minnesota switched from a caucus in 2016 to a primary in 2020. Turnout increased from 200,000 votes to more than 700,000, so we can't say that Sanders lost his base of support from 2016 into 2020 (in fact, he got almost twice as many votes in 2020). One theory is that Sanders has a "more enthusiastic" base, and caucuses draw the most enthusiastic voters because of the time burden a caucus requires. Relieving this burden and increasing voter turnout is likely to blunt Sanders' advantage.
Also, 8% of Minnesotan ballots in 2020 went to candidates who had left the race as of election day, mainly because of mail-in voting. Another 13% went to the 3rd and 4th placing candidates, because in 2020 there were two more major candidates (with >1%) than in 2016. This complicates a comparison to the two-candidate race in 2016.
And as others have made clear, Sanders' main "moderate" opponent is different in 2020. Clinton's net favorability among Democrats in April 2016 was +36%; Biden's net favorability among Democrats in February of 2020 was +49%.