The original excuse I believe was that he felt uncomfortable about aircraft emissions for such a short trip. I'm not sure that adds up, if you go for a weekend or a month the emissions are the same. Also I thought climate change was his dad's pet project, William's being homelessness.
As others have said he probably just didn't fancy it, which is really poor given he is president of the FA. This event is one of the biggest to have happened to England and the UK for god knows long and he turns his nose up at it. He should be there, I mean, what else is he for if not for doing stuff like this. No excuses, he's been ****.