My old pal John Judis has some ideas in a piece on Talking Points Memo. I don't agree with everything here but it's all worth thinking about. So toss that article about exit poll results in the circular file and take a look at what The Curmudgeonly Leftist™ has to say.
"Why did Democrats lose some seats in the House, but retain their majority? If you look at the particular elected Democrats who lost or almost lost seats, especially those in districts Trump had carried in 2016, they were hampered by the national party’s identification with demands to “defund the police” (which most Americans outside of a few zip codes saw as a threat to public safety), House Speaker Nancy Pelosi’s failure either to achieve a deal on a stimulus bill or to make sure that the public blamed the Republicans for the failure, Biden’s threat to “shutdown” the economy in the face of the pandemic (which frightened Americans who are worried about losing or have already lost their jobs), the party’s support for a Green New Deal and opposition to fracking, and the specter of socialism (understood in South Florida as Cuban Communism and in other vulnerable districts as “socialized medicine.”)"