They have very full days, going to different places in the country, eg one visit in the morning, somewhere else lunch time, another place in the afternoon. Evenings too. I certainly couldn't cope with all that travelling, I'd be worn out in five minutes!
If you look at the number of engagements they do, and info about those engagements, it doesn't equate to "very full days" very often. Maybe sometimes in tours and things, but not every day.
Often they'll do a single Zoom meeting or a single phone call as their only engagement of the day. Maybe two or three Zooms in a week, and often they'll go weeks between engagements. There have been times when royals have done a single engagement in a day and left after 20 minutes. So they'll work for 20 minutes (maybe an hour if you include getting dressed and travelling and that's being generous) and that's counted as a day's work.
Events like attending the Wimbledon final, taking their kids to the panto, attending the Baftas, or even attending family events are all considered work engagements and count towards the end of year numbers.
I respect the Queen and Anne's work ethic, but the younger royals are just very workshy. Kate's first patronage had to close its doors due to lack of funding last year, and it came out she'd literally not visited them once since she first became patron, despite the charity seemingly meeting Kate's interests (art and children's well-being) perfectly, and Kate using the excuse of taking her time to pick the right charities so she could carefully select charities that she really cared about and could be hands on with, when the press were criticising her for taking more than a year to start appointing patronages.
Last year she did a Zoom call with a different one of her patronages and it came out then she'd not visited that charity since the day she first became patron, either. That's shockingly bad. But at least Kate did her Chelsea garden, and has been high profile in talking about early years which she clearly cares about. What does William do? He sometimes talks about mental health or racism in football, but at nearly 40 he has no major projects or initiatives to his name the way Philip had the Duke of Edinburgh scheme, Charles has the Princes Trust and Duchy range, Harry has Invictus and Sentebale, even Camilla has her project supporting rape victims.
The RF don't need Zara or the York girls, they just need Will and Kate to start pulling their weight.