It happened because the Left chose to vote their individual conscience, including abstaining from voting for imperfect candidates, as if Politics was a negotiation rather than a winner-takes-all race. Biden was not my first choice, but he's a fuck ton better than what Trump would have done in a second term. The Clintons are unabashed globalists, but still a fuck ton better than what Trump did in his first term.
Not just follow that down the line to Senators, House Reps, State Governors, State Reps, County boards, School boards, Sheriff - you name it. There are zero points for second place and liberals vote as if they will change the Democrats by withholding their support for candidates they don't agree with. Boo fucking hoo. Hold your nose and vote for the team that's the closest, because a non-vote is equal to half a vote for the opposite side (insert baseball half-game lead/trailing description here).