The way Facebook and Twitter censored the Biden story was a bit too obvious. Makes me think that they probably want Trump to be re-elected. They're just riding on the rhetoric of the last election; people will vote for the candidate which Big Tech doesn't want to win. So if it looks like Big Tech hates Trump (I.e. helping Biden), then people will vote for Trump.

Or maybe I'm overestimating the intelligence of people who work for Facebook and Twitter?

Maybe they're not very smart and they think that censoring the Biden story will help Biden.