There's nothing to suggest that Kate isn't interested in fashion. There's a whole team of people involved to make sure she looks great and she's had stylists, seamstresses, tailors and style consultants on her payroll.
She's worn all the 'hottest' and best designers whether it's clothing, shoes, hats, bag, jewellery, etc and had many custom and bespoke pieces made. There's definitely been many items or designers worn whilst they've been popular, new, trendy, etc.
There's also an effort made for many of the outfits to be appropriate or timeless or classic or whatever (not that we can really predict how well clothes would age).
(Not saying any of this as a criticism!)