She may very well lose still but Hillary had major likability issues and a corruption perception from 3 decades in the public eye. They also were able to make Benghazi and “but her emails” stick as scandals. They haven’t really made any particular scandals stick with Kamala and she has way less baggage. 

The other thing is Dems were complacent because a lot of dem or dem-leaning people thought “there’s no way Trump actually wins, I don’t really like Hillary so I’m not gonna bother voting or gonna protest third-party vote.” This has now created a very panicky Dem electorate that always feels they’re gonna lose which is hopefully a good thing in getting their voters to turnout. 

And not that it matters a ton but I think Walz has been a much better and effective pick than Kaine and Kamala seems to be doing a lot more rallies and campaigning in the states that matter the most (Hillary spent a lot of time and money in Florida, Ohio, Iowa, even Missouri, tho in her defense we didn’t realize yet how rightward they’d all trended).