I find there are several reasons for the wishes of people today. Perhaps my view is determined from where I live & the clients I attract, culture, income, age of clients and other ingredients.
Brides today get information from various sources including, friends, magazines, movies, T.V., the internet and, I believe to a lesser degree, family including relatives. Religion can be a factor but I find less so amongst people who hire me.
Brides want to look beautiful. They get the idea/concept of beautiful images from the sources I mentioned in the above paragraph. They see very few, if any, of the photos mentioned in the first two posts, other than what parents or grandparents may have. They think the photos look stiff, unnatural and not a part of what they want to see of themselves. Whatever I think or you for that matter, in business if you're trying to earn a living in the photography profession, beauty is in the eye of the person who has the checkbook. If you want to stick to principles/art be prepared to work hard finding potential clients who share your vision or have a day job to support yourself.
Attitudes have changed. Technology has allowed it as back in the 1950's when I started in photography I couldn't make photos like I can today.
I make photos with more of a style clients want but I still use classical portrait principles that my mentor & coach Monte Zucker taught me.
Telling someone to look happy is quite different than catching them when emotions peak and they show it and want to see their wedding day as a happy day, full of little emotional blips that they want captured with photography. I advocate group photos as well. You are correct that they are important but the others are important to the client.
These people, my clients, generally, are not actors. Acting is difficult. That's why I capture them when they are happy because it won't look the same as if you tell them to look happy.
That's why I love the wedding photography business. So much variety within each wedding and each wedding is a unique event as the people react in so many different ways.