Totally agree @queenofarles
Personally I think Kate is a busy mother of three young children and has neither the time nor the inclination to lie around having beauty treatments. I'm pretty sure she did her own makeup for her wedding for instance, I remember reading some criticism of her decision.
She is naturally slim and athletic so it is easy for her keep her figure. I highly doubt she has "fitness experts" or even a personal trainer. Her siblings are sports/fitness mad so it's not as if she can't get advice. I expect she has a running and/or rowing machine where she can exercise in peace and privacy without the risk of being accosted out running or having spy camera Lenin the gym as happened to poor Diana.
Keeping her figure means she can pull out something she wore some time ago confident in the knowledge it will still fit her. Just as Princess Anne does.
"fashion houses desperate for you to wear their clothes" ???
She sticks with the fashion houses she knows and trusts. Why would she want to be used for free advertising by any old fashion house keen to make use of her image? And risk being persuaded to wear some hideous outfit. She's not stupid.
Sure. She doesn't have to polish her own shoes or take her clothes to the dry cleaners. And her dresser/assistant does her hair, she probably has someone else she goes to from time to time. So what?
Same goes for lots of other women who like to be well turned out.
You only have to look at Oscar's night to see how badly wrong it can all go if you leave it all to the "experts".
It's just all part of the mean spirited trope on here that she's lazy, sits around being hand fed peeled grapes and wouldn't even look attractive if she didn't have an army of assistants at her beck and call.