I think you are right @Bertrand and @Encyclo.
Also, ultimately, I just don't think Kate is that into clothes. She dresses well and appropriately - never misses a beat, on duty or off, really.
But she's never going to set trends or be edgy. That's not her thing.
Who knows what her thing is - maybe it's sport, maybe it's family. Maybe it's stamp collecting or growing spuds or share trading 🤷♀️.
It could even be walking three paces behind her husband. Whatever... that's her business. It doesn't seem to be looking like a clothes horse though.
(Not sure that excuses 100 coat dresses in forest green, and a dozen others in Kermit green, but - again - that's her choice),