
I think her sense of 'justice' is what made them fall in love. The person she was before marriage might differ from what she is now, since before she was just a saintess, so she could preach anything she want, without doing anything about it. Now that she became a crown princess, she has the power to do what she preaches. But she doesn't. She still only yaps about 'justice'. The only thing she does is live the stingy life she did before marriage, but only when it comes to food.
So the MLs started to notice that she's just a professional yapper. She doesn't respect others, especially nobles, which is awkward since she now works with dealing nobles and commoners plights.(Which I don't think she works at all)
She called hestia selfish for not giving soap for free, but she doesn't even try to make soap and give them away free. She expects others to do things and let her decide on what others do with their lives. These traits probably only showed up after marriage, because during dating, your don't really see all sides of the person sometimes. I think that's why they fell for her. They only saw the yapper side of her and thought, 'shes not like other girls'
Uum how did kael and the crown prince even come to like Diana? She's extremely selfish, naive and incompetent. Both men seems to enjoy eloquent and down to earth women so...how