Same way we all form opinions of those we don’t actually know … it’s not based on any true reality, more it’s a vibe.
I’ve just always found William to be going through the motions. I accept this is my interpretation, but he has a light work load compared to other Royals and I still sense he resents the job. Really, he’d love to be a Trustafarian like his mates - all the money, all the status, none of the work. I know a good few old Etonians who have more than one large property in the UK and abroad, staff and funds. They ‘work’ on their estates and have a lovely time heading into the City once a month to visit their mistress club.
I’ve always been torn on Catherine - I get the need for her to be the absolute opposite of Diana but that is the Institutions need. The family business ruling the actual family (Harry’s main complaint).
I find her so bland. She’s either so ‘eyes on the prize’ that she’ll accept anything, including putting all of her needs and personality second, or shes so totally devoid of personality or agency that she’ll accept it. Neither of these are traits I find attractive.
I get that some may say she loves William so much that she’s prepared to (and has become brilliant at) subverting her needs but again, that’s not a trait I would encourage in a daughter or similar.