I’m not convinced the reason for today is Andrew however I think from past actions we have seen that William feels very strongly about Andrew not being seen to represent the Royal Family officially but will toe the line for his father for family occasions, and for the time around the Queen’s death when he was helping his uncle deal with his mother’s death.
So he drove Andrew, Edward and Sophie to Balmoral the day the Queen died, and he drove Andrew to church from Balmoral on one of the significant anniversaries/family gatherings after she died - presumably on the request of Charles to show family solidarity.
It was reported that William gave a me or him ultimatum over an official calendar engagement - can’t remember which one now and Andrew wasn’t allowed to attend.
So I wonder if he’d made a similar ultimatum about this event which is sort of a private family thing but very public so could be seen as somewhat official representation.
Maybe someone called his bluff - Charles, the Yorks themselves? And he wanted to show he wasn’t joking. I’d like that to be the case - Charles is being way too lenient with Andrew and it’s damaging his reputation.