I don't mind William so much cos at least doing search and rescue he's contributing to society. Its not like he's laying around on his arse when he's not in the public eye.
Kate is an individual who I struggle to understand. She was notoriously indignant at the "Waity Katy" tag and her people went to great lengths to assure the media that she wasn't actually long-term unemployed but contributing to her parents business. 
You'd think then that stung by that, she'd have gone "right! I'll show them!" and gotten stuck in immediately, like Diana did. But even before the kids there'd be literally several weeks between engagements. We were told she was "taking her time deciding what charities to honour" and all that. But it was terrible, terrible, terrible PR.
Now she has 2 kids and if she had been a workhorse all this time I'd be totally generous about her reducing her workload a bit. But you can't really reduce it any more than before really, can you?!
So it looks for all the world like someone who was just biding her time before she bacame a Mum and had an excuse to nestle at home as much as possible.
And whilst a lot of people want to be SAHMs, thats not the family she married into. She married into a family where regardless of kids, you do a couple of hundred engagements a year till you keel over.
Tbh, I don't see how she does so much less than Sophie of Essex, who also has two young kids and seems to have an engagement most weeks.