I'm sure it's been said in here already, but Sunak made a point of saying "I went to all the UK based D-Day commemorations" when being challenged on this
I think he thought that he'd get a pat on the back for "sticking it to the EU and Biden" by not staying, but didn't realise that this is a topic where most people aren't as anti-Europe or anti-American. Those folks fought along side us, and died along side us, in the quest to liberate Europe from the clutches of the Nazi's. This is the one day of the year where even most of the right wing flag shaggers are happy to stand alongside with people from other countries, because we really were all in it together and really were fighting something worth fighting
He's badly misjudged the reaction, and is either poorly advised or an outright buffoon