Agree, it was basically an arranged marriage.
Considering that he was at least vaguely familiar with her because he'd dated her sister, which obviously wasn't a love match, I believe he picked her out because of her blueblood family tree, her youth ( the virginity issue which was reported in the US as still being a factor in the 80's), and of course, her absolutely natural beauty. Even when she was a caregiver to a child or children at 17-18, it was clear that she was very pretty and would grow into a great natural beauty.
( I'm aware that her hair was professionally lightened, but that's not what I mean at all). Diana had marvelous bone structure, flawless skin and incredible eyes which are all so clear in her earliest photos released as soon as she was known to the public because of their courtship, then engagement and fabulously extravagant wedding and so on and so forth.( I have my copy of her last magazine cover before her death, although I really can't look at it, even now, and she was so stunning in a casual high neck sweater in a B&W photo.)
Then, when they did meet, she, extremely shy, asked him a very kind and thoughtful question about missing his great- uncle and personal mentor, Lord Mountbatten, who was murdered by an IRA bomb just a year or so previous.
I believe her shy, kind consideration of his feelings was what touched him most, and pushed him from the " Nice girl. Maybe one day." to a very fast engagement.
I wish they had been more compatible, even if it was an arranged marriage in some aspects, and formed a loving and lasting bond. She'd be alive, we'd have had her in this world for the past 20 years and going forward. She and Prince Charles might well have grown into a loving, compatible, faithful couple for all his life, which would have been so wonderful.
Funny future king George, darling Charlotte, and little Louis would know a fine, loving, generous grandmother. Kate would have a true blue RF companion and friend as well as a still- young and fun mother in law.
Most of all, BOTH of her sons would have had someone who didn't handwave their activities like Charles has admitted he did when they needed guidance and support. This is especially true for Harry, who has said in interviews that he really doesn't remember all that much about her as far as many specific events in his childhood due to his young age when she died. I think he would be a much different person, confident and with a great deal of common sense and self- direction, had she had a hand in his child to teen to adult life.
I STILL can't look at a photo of her or discuss her without thinking " If only" and my eyes tear up. There'll never be another English Rose who surpasses what she represented, the good she did for worldwide acceptance of HIV+/ AIDS patients, which definitely raised both awareness and funding for major research which has changed and extended many lives incredibly, and so many wonderful charities of which she was the world's most influential royal patron during her lifetime. Long may she be remembered for the unselfish love she gave to the least fortunate in full measure for as many years as were hers to live.