Slow dancing's death as a sign of falling trust and stunted social growth
Most people at dance clubs, even young people, don't actually dance with anyone else anymore. Now everyone hangs out in their own small groups instead of wanting to mingle. That's the opposite of what you saw from the late '50s through even the early '90s, where socializing between boys and girls was the main reason you went to your school dance.
I still vividly recall my first middle school dance in the fall of 1992, when I was in sixth grade and had just turned 12. Even though there was a bit of sex segregation, there was still a sense of urgency to break it up and just put yourself out there -- c'mon man, just go up to her and ask her to dance! Anyone could tell that the girls were also eager to break free from their comfort zone and actually get to touch a boy's body with their hands for a decent stretch of time. During the '90s that sense of urgency evaporated as young people, in all aspects of their thinking and behavior, switched from a "now or never" mindset to one of "let's just goof around and put the big things off until later."
Everyone has commented on how vulgar the YouTube videos are that show young girls dancing, or how scandalous it is that young people's preferred dancing style -- when they actually do dance with someone else -- is grinding, which resembles a standing lapdance. Yet these changes signal young people's retirement from libidinous behavior. Girls shaking their ass around in an exaggerated way are just trying to get as much attention as possible without having to give anything in return. During truly promiscuous times, girls have no such self-consciousness and feel powerless before boys. Just listen to any song by the girl groups of the early 1960s, Bananarama, Belinda Carlisle, and the "mall queens" Tiffany and Debbie Gibson. Girls at dances back then weren't gyrating around wildly but drifting around waiting for some boy to sweep them off their feet. They gave off a signal of vulnerability rather than control.
As for grinding, nothing could be more anti-sexual. The girl is not even facing the guy -- therefore they will not be making out, let alone fucking, as they haven't established the most minimal level of interpersonal contact -- namely eye-contact. While she may or may not let him put his hands on her hips, she herself rarely touches him with her hands, also spelling doom. Also, she is free to just flit away on the slightest whim to someone else: she just has to step forward. When people dance face-to-face, she would feel a huge psychological cost to bail out in mid-song -- she's been caught in eye-contact, facing another person, for awhile, and she'd have to step back, turn her body completely around, then walk off. Under the circumstances, that's just too much, so she's guaranteed to stick around for at least the full song, and maybe a few others. There's no such guarantee with grinding.
Finally, this applies to her friends meddling in her business, too. If it's face-to-face, her friend would have to make a very rude cutting-in gesture, try to pry her hand from his, spin her around a bit, and then lead her off. That's too rude for most people to attempt, so her friends will leave her alone in that situation. With grinding, they can just walk up to her, take her unoccupied hand, and lead her off without having to turn her body around, make her step back, or otherwise cut in between two people, all in a single motion.
Add it all up, and you see a profound lack of trust between the sexes, especially how girls feel toward boys. It takes a certain amount of good faith in the other person to dance face-to-face and close-up, given how locked-in you will be for at least several long minutes. Grinding signals her unwillingness to place even that much trust in him -- she doesn't want to establish eye-contact that might pull her in, and she wants to be able to bail out whenever she pleases and without warning. This is just one aspect of the decline of trust in others that has showed up in social surveys since the late '80s / early '90s.
Girls have always felt uncomfortable by making themselves vulnerable, but it's only recently that they've valued immediate comfort over the longer-term benefits like establishing a bond of trust between herself and a boy, making a deeper emotional and perhaps physical connection with him, and so on. Sure, you expose yourself to the risk of being used or having your heart broken, but girls used to accept that risk -- and indeed did occasionally get used or had their heart broken. They simply accepted those losses because otherwise they could not have enjoyed all the times where something deep and magical happened. Now they want to be shielded from every tiny threat to their comfort zone, preventing exploitation and heartbreak but also stunting their emotional, social, and even spiritual growth.
One last thing about grinding -- aside from these problems with trust, eye-contact, etc., just look at how little physical contact there is! The middle section of her ass touches the guy's lap, and that's about it; at most the guy's hands might also touch her hips. Slow dancing places one body right up against another, often bringing their heads close together as a prelude to kissing, as when she rests her head on his shoulder or chest.
I wasn't alive to see what dancing was like in the mid-'30s through the mid-'50s, when the crime rate was falling and people were generally behaving themselves, but from what I've seen in TV and movies their dancing was pretty emotionally detached and somewhat physically at-a-distance as well, although at least they were facing each other. It doesn't look exactly frivolous, but you can clearly see the lack of abandon or connection there that we'd recognize at any young people's dance club today.
Part of the reason why girls were so willing before to make themselves vulnerable was that they felt like the guy was not in full control of himself either, and therefore could not coldly plot out some calculating scheme to use her. And he felt this way about her, assuaging his worries that she might be a maneater or someone who'd otherwise leave him heartbroken. Thus, both trusted each other and did not feel that either one really had the upper hand -- they were simply being moved around by the hand of fate, a neutral third party. Hence the ubiquitous phrases like "I just can't help it," "Let's not try to fight it," and so on. If you want to reap the benefits from close social interaction, at some point you have to switch off the rational, lawyerly part of your mind and just go with the flow.
The music that young people dance to reflects this -- Frank Sinatra and Ella Fitzgerald sound more cool-headed and composed than the power balladeers of the 1970s and '80s. My impression is that these kinds of songs are the most likely to have been forgotten even for bands that have seen a revival of their popularity, and even if the song was a #1 hit such as Madonna's "Live to Tell" or The Bangles' "Eternal Flame." The last slow song in the classic style, that I can remember, is "Come Undone" by Duran Duran, released as late as 1993. So, in the interest of historical conservation:
"Save a Prayer" Duran Duran (1982)
"Total Eclipse of the Heart" Bonnie Tyler (1983)
"Amanda" Boston (1986)
"Take My Breath Away" Berlin (1986)
"Heaven in Your Eyes" Loverboy (1986)