Probably doesn’t help that the administration has used Kamala as the bearer of bad news. Any time bad news gets released, it’s coming from Kamala instead of Biden. Because the administration wants to keep Biden’s nose clean, but that comes at the expense of Kamala.
There’s also the fact that even when they have absolute control by the numbers, reality doesn’t really reflect that; The democrat party is not united, and is full of politicians who will refuse to follow the party line unless the party bends over backwards for them.
“Oh, you want me to vote to stop fascism? Sure, I’ll be happy to do that, as long as you add funding for a brand new bridge in my home state.” Repeat ad nauseam until you have a horribly bloated bill that nobody actually wants to vote for.