Democrats have often failed to address the needs of their most important base of voters : African Americans, so when organic black centered movements like #BlackLivesMatter
and #DefundThePolice arise Dems fail to act which makes it easier for Republicans to define the issue

Remember "progressive" candidates like Sanders and moderates like Clinton were essentially saying "All Lives Matter" throughout much of the 2016 campaign https://www.vox.com/2015/7/20/9001639/bernie-sanders-black-lives-matter
So when even the 'progressive' wing of the party ignores or dismisses discussions of reparations and #BlackLivesMatter
for YEARS and now in 2020 #DefundThePolice it's not hard to see why there are challenges engaging young black voters and activists

Black people still came out and voted in historic numbers, mostly for Biden, in order to end the tyranny of Donald Trump, but if you want folks to keep that same energy you can't treat specific movements emanating from your base on the sidelines for two cycles
In 2016 if you were a white Democrat and said "Black Lives Matter" everyone said it would kill you in the suburbs. By Summer 2020 I see more #BlackLivesMatter
signs in suburban DC yards than I saw #BidenHarris . Embracing your base helps more than it hurts

Support for "Police" is often a proxy for anti-black sentiment, and there are almost NO Democrats who've ever run on a #DefundThePolice message, it suggests catering to people who are concerned about defunding the police is a fool's errand https://news.northeastern.edu/2020/06/09/the-black-lives-matter-protests-motivated-voters-in-2016-will-they-do-the-same-in-2020/
Protests about #GeorgeFloyd exploded across the Minnesota and Wisconsin. Yet Biden won both states handily. If arguments over police reform are such dangerous messages they certainly didn't stop those states from flipping