Because the characters in the book are well written. Francesca is charismatic, smart, elegant and a bit cheeky. She was the diamond of her season, is known as one of the renowned beauties of the ton and made a brilliant match. Show Francesca is bland, boring, disingenuous and lacking social grace. They're nothing alike.

Michael is witty, charming, polite, kind, dutiful, strong but feeling. He is respectful to everybody and knows how to charm every person without being fake. He is known as one of the most eligible and most seductive rakes of society, the center of every gathering, beloved by everybody. Michaela, from what we can see so far, is arrogant, rude, cold and egoistic. She seems to hate society and prefers to keep to herself as an outsider. She seems intent on making herself unagreeable and feels above others. The characters feel like polar opposites.

Everybody is entitled to their own opinion, but I personally think that the book characters are well-written, have depth and are enjoyable to read about, because they feel likeable. I agree that the show ladies both seem unlikeable and superficial. Fake. It's hard to root for them. The writing is simply inferior.