Posters on various threads have commented on the difference between the relative openness of Charles and the relative caginess of Kate and have suggested that it's partly because he is head of state, so we have more of a right to know.
The other big difference between them is that she has young children and he doesn't. There is a possibility that she has something very serious, life-changing or even life-limiting, so they are being very careful about what they tell the children and when. In that case I can understand that they would not want speculation in the press and on social media about her condition and supposed prognosis. Maybe they are trying to avoid the children seeing headlines like TRAGIC KATE'S KIDNEY FAILURE - PRINCESS MAY HAVE JUST MONTHS TO LIVE
Plus endless comparisons with her MIL, speculation about who William would marry next, whether Harry and Meghan would come to Kate's funeral, was this caused by the stress of being labelled racist, or could this be the turning point for the brothers etc etc etc etc etc
I mean it's bad now but this scenario would be so much worse if you're trying to protect DC.
So maybe it would be better and kinder for now to assume that the family is going through something pretty shitty and leave them to it. If not, I'm sure she'll be right as rain soon enough and everyone can go back to speculating about her marriage, mental health, eating disorder, laziness, poor public speaking, Botox, choice of university, hair, dress sense, parents, children, sister, piano playing etc etc