Thank you, Iceflower.
There was a brief segment on the 12.00 news and apart from Mary not being there and the presence of quite a number of Australian reporters, this court went ahead as usual.
Okay, in order to answer that question, we need to go back to the mindset people had when this tradition started, back in the time of Absolutism.
Joachim do not attend, because he is not the Crown Prince.
These courts (apart from the diplomatic and the court for the government) are for high ranking civil servants and military personel, who have this opportunity to say hi to their boss. Their boss is of course the Monarch, and the future boss is the Crown Prince, and it's good idea to greet both of them - and to let them get to know
you are....
From the perspective of the Monarch it's also a statement: "Hi, I'm your boss. - This is my son, and he'll be your next boss. Just in case you should be the least bit in doubt"!
Having a junior prince present, would send out a confusing picture: - "Did you notice Prince Joachim was there as well"? "Yeah, odd. Perhaps the Crown Prince is no longer a favourite of Margrethe"? "Hmm, might be a good idea to suck up to Joachim instead". Get the idea?
From those who go to a court it's also a statement: "Look at me. I went to a New Year Court. - Yep, that's how important and high up the ranks I am".