I can think of a few worse things to say about her (narcissistic, self absorbed, obnoxious...the latter which seems to have rubbed off on Harold).
His wife’s quotes: making a Mandela comparison (celebrations in South Africa for her trivial wedding were akin to the day Mandela was released from prison), throwing people of African background under the bus (“I was ugly with frizzy hair”...yes because straight European hair is the definition of beauty), and the me me me in the Oprah “interview”, she’s a deeply unpleasant character so no wonder William and Kate can’t bare the sight of her.
There is also a cultural divide here between nationalities.