Could you imagine even if he did attend? Let's go through how a normal President would act and what we'd get with Trump:
The President-Elect and First Lady arrive to the White House where Trump and Melania would greet them. Trump would stand there with his arms crossed while Melania looks stone faced as she usually does.
He offers old, frozen Trump Steaks long past expired, along with two First Class Tickets that are no longer valid on Trump Airlines to any closed Trump Casino of their choosing, and two free courses to Trump University.
Trump gives a tour of the Oval Office, and he has no idea what goes where, because he's never done the job as President. Biden actually shows Trump where things are at, because Biden has been there before with Obama.
Biden leaves to be Inaugurated, while Trump steals the silverware and leaves a note to Biden that reads like a tweet.
No thanks.