I will use this picture to illustrate the difference in thinking between most Americans and the British. Look at how similar the ladies look. They are wearing similar colors and styles. All except Meghan. Now look at the men. Basically clones of one another. They are already wearing suits which makes them look the same. But they also matched the color. No individuality. That’s the answer to your question. Americans are socialized to believe in their individuality. Most of them have a difficult time conforming to rigid rules and protocols. To Americans, that makes little to no sense. Meghan believes it’s her individuality that makes her special.
For me as a guy with an English mother but, born and raised in the US, I understand why the Royal family thinks they have to look similar in the photo. But as a guy, it makes me want to turn away when I see how much like clones the men look. I don’t think they look nice or handsome. To me they look like a security detail in uniforms. But somehow this has become the standard of dressing up. It’s very archaic. In comparison Meghan looks like a diamond in the rough to me. Someone who did something different. She has a differnt perspective.