The Democrats knew this was a one term presidency.
Riding the wave of anti-Trumpism, with both houses and the Presidency Democrat, the goal was to further "fundamentally transform America."
That is why they are passing as much legislation as they can in two years, before the traditional flipping of Congress to the opposing party.
It doesn't matter who is in the White House, as long as he signs the bills into law.
Biden is not the leader of the party. He is a figurehead.