When asked if leftists were going to pack the supreme court, why did Biden answer by rambling on about "People need to go vote"?

Biden can only say what he's told to say.

maybe he misunderstood the question

Do you have a problem with people voting?  That's the immediate issue, not a contrived issue about a change to the court that probably won't happen anyway.

it was the top cue card

he memorized his script in the wrong order

Because if people knew the truth about Democrats they wouldn't vote for them.

Democrats are panicking cause Trump can make the court conservative for a long time

If Biden says yes to that idea he loses many Centrist Democrats and Independent voters who are appalled that politicians would politicise the judiciary. If Biden says no, he loses the votes of Progressives. Why would Biden refuse to talk about his policies. Because Biden knows that whatever he says will alienate some segment of the Democrat party. Why else does Biden refuse to talk about the policies he would enact if elected president. "I'm not going to answer that question" isn't what Americans want to hear from a presidential candidate.

He's a DNC puppet. He can't go against the wishes of his black supremacist party.