If all the Independents are siding with Biden, which seems to be the way it’s going, of course his enthusiasm is lower on average.
Independents are always being given a choice between two things, neither of which they really like. In this case, the fact that ALL of them plan to vote for Biden means he will win the election handily.
Also how about this little jab at "B"lack people:
"... roughly 1.7 million low-information left-leaning voters largely women of color under 35"
They don't have much respect for their voters or black people. I meant it may be true but ... I wouldn't talk about my own hoped for constituency with a mild euphemism for 'ignorant.'
https://www.cnn.com/videos/politics/2019/03/05/joe-biden-tough-on-crime-speech.cnn