Or it could be that it was a doomed, difficult, and troubled marriage because they lacked emotional intelligence and interpersonal skills. The way I look at it, they didn’t ruin two marriages so that is a positive.
I find your view super judgemental, although of course you are entitled to your opinion. So many marriages are difficult and troubled, and perhaps doomed as well. I don't think every person in such a marriage is lacking in emotional intelligence and interpersonal skills. Marriages often fail because of a lack of compatibility and a lack of shared goals. And sometimes people change and love just fades away.
OTOH, there are plenty of people in miserable marriages who stay married for their whole lives because divorce is taboo, or 'for the kids', or in the case of women, because they have no means to survive/earn income on their own.
Diana was very young when she married, and it's not hard to understand the allure of becoming a princess and having a fairytale wedding. Lots of young women make mistakes in romance. It must have been exceptionally painful and lonely for her to have been married to a man who was in love with someone else. SFAIK, she handled her situation with grace and dignity, although did harm to herself through builimia.
Yes, I know Diana was young when they got married, but she was old enough to have two teenage or preteen sons when they got divorced.
Girls can have children at 12, 13, 14. Having children is unfortunately not a sign of maturity.
Both Charles and Diana owed it to their kids to put on their big boy/girl pants and deal with their differences without airing their dirty laundry in public or scaring their children. They were apparently incapable of doing that.
Airing dirty laundry in public goes hand in hand with being a royal. Loss of privacy is one of the big costs that royals pay. And if there is no dirty laundry, the media will drum some up.
Also, William and Harry have grown into decent young men, or at least appear to be. Their parents played a role in that.