They didn't have all the racially motivated riots during most of the primaries. Plus, with everyone dropping out right before super Tuesday and virtually giving the race to Biden at that point, a lot of people were discouraged about voting.
Also just saw today that The Chamber of Commerce, the largest lobbying group for businesses, is in favor of a Biden win, and a Dem Senate majority in addition to the 23 Dem candidates in the House that they are donating to.