“Those people don’t vote for me. Why should I?”
BREAKING: Asked if he planned to pay his respects to late civil rights icon Rep. John Lewis, who will lie in state at the U.S. Capitol, Pres. Trump says, “No, I won’t be going. No.” https://t.co/ri9eENlkAQ pic.twitter.com/JjGiPgHeju
— ABC News (@ABC) July 27, 2020

Trump holds a grudge. Always has. Plus he’s a White Supremacist.
AG Bill Barr claims that he’s not Trumps “factotum,” or in street language, his handyman and fixer.
That was a role previously played by Michael Cohen, federal prisoner #.
If Bill Barr actually believes that his actions are benefitting “We the people,” rather then mostly benefitting his master Trump, then this country is in even worse shape then it’s most ardent critics claim that it is.
Sure, it was a dick move, but all for the best as there was no way his presence could do anything besides sully the occasion.