It's a combination of factors, isn't it? The RF used to engage as much as was necessary to keep the press at bay. The Queen was famously stoic and kept family affairs quite private.
The younger generation of Royals have tried to become more relevant and engaging. Times have moved on and instead of the odd photo, developed in a dark room, hundreds of photos can be taken in seconds.
Now, there are medical concerns and the RF has asked for privacy. But privacy is an illusion and you can't have it all. You can't be a figure if public interest and keep your privacy. It's just not how modern society works.
It would have been much simpler for KP to give occasional bland updates about the health of Princess Catherine. They could easily have said 'She's out of hospital and is now recuperating. She thanks you for your concern and well wishes.' 'She's doing well and her recovery is progressing as expected. She thanks you for your concern and well wishes.'
If they had done that, they would have avoided a lot of speculation. I'm so glad I'm not a Royal.