I find it sad that Prince Michael - who is President of the Royal Kennel Club (the right to use Royal was given by Charles III back in April) - wasn't even mentioned in the CC for this event. I know he isn't a working royal but when he attended Garden Parties under QEII he was mentioned and if he attended an event with a royal when he was the Patron etc he was always mentioned in that role.
But where was did the expectation that all four of the Wessexes and Yorks would become working royals come from? The precedent that was set by the previous generation was that only the eldest child would take on royal duties. Princess Alexandra was an outlier due to the number of young working members at the time. Only two of them would have likely joined the roster if that norm was put in place.
The Wessex children were never expected to be working royals - hence no royal titles from the get-go.
Beatrice was the one who was raised with that expectation and my information is that she confirmed that idea with the late Queen, Charles and William numerous times while going to school and again before university but just as she was about the graduate she was told 'not wanted or needed' ever so she went and did some more courses, got a job and made a new life for herself.
Charles now has to face the very real prospect of either changing his mind on Beatrice or having Louise start using her HRH and become a working royal. I suspect that the latter is more likely simply due to her age and due to Beatrice's parents and the fact that she is largely despised by the British public due to the way the press have presented her over the years. She may personally have not done anything wrong - unless wearing hideous clothes is wrong - but her parents mean she is disliked simply for who she is and not what she has done.
The third option is to wait until George has finished his education and military training in about 20 years and Charlotte the same (or not let one or both of them even have any post-school education or life). William didn't become a full-time working royal until he was 35. If George is given that same time frame it is a quarter of a century until a new working royal will join the roster full-time. I suspect he will be working as a royal from age 18 with education and military training as a secondary part of his life ... as it was for Charles rather than as it was for William.
Charles, for instance, was undertaking royal tours while still at uni e.g. 1970 while finishing his final year at Cambridge he also joined his parents and sister on a tour to Australia and New Zealand for the 200th anniversary of the voyage of Captain Cook (NZ 12th-30th March and the Australia 30th March to 8th April and from the 9th to 14th April he was visiting Japan to attend Expo). He returned to the UK to prepare for his final exams before graduating in June that year.
Charlotte will probably be expected to be a working royal from finishing school as well while Louis may be allowed to have a longer time - possibly getting to have a 20+ year career in the military or whatever. He may be freer.