Booker: "I confess that I have been imperfect. I confess that I've been inadequate to the moment. I've confess that the Democratic Party has made terrible mistakes that gave a lane to this demagogue. I confess we all must look in the mirror and say 'we will do better.'"
NPR also mentioned that there just hadn't been that much going on to filibuster. Nominations, sure, but Congress has been mostly taking a back seat to the presidency, for better or worse given executive actions aren't as permanent as Congressional law.