I see it as just the opposite.
Humans have changed little. Morality has improved somewhat, but it has been far outstripped by our technical abilities.
Take WWI as an example. Violence and war have always been part of the human situation. But for most of human history violence was a handicraft. You pretty much had to kill people one at a time with hand tools, like swords. Then EuroChristians weaponized gunpowder, greatly facilitating slaughter. And made advances in navigation technology and ocean going vessels. That brought EuroColonialism, and the attendant horrors to the planet. Horrors like slavery and genocide on a global scale. One of the big justifications for that was "Bringing the Light of Jesus to the benighted darkies around the world."
By WWI, industrial capacity, technology, and fossil fuels really ramped up mass killing abilities. Unfortunately, humans were still prone to violence and mostly still operating on moral codes from primitive cultures.
The problem wasn't that morality had changed, it's that it hadn't.
Similarly, sex/marriage/procreation has changed dramatically over the centuries and moral codes haven't kept up. For most of human history, kids hooked up in their teens and started making babies. But the likelihood that both of them would survive into their 30s was slim. Marriages weren't expected to last more than a decade or two. And children were an economic asset. Nobody expected parents to provide health care and education, then send them on their way upon reaching adulthood. Kids started earning their keep while in single digit age and then provided for the parents who were still alive when they're grown. So, while the world has changed enormously, human instincts towards sex have not. And the moral codes were invented in a completely different world. Overpopulation is a far bigger moral issue than having your community wiped out by a drought or epidemic.
Humans and morality have not changed, but the world has.
Humans and morality haven't declined. Quite the opposite, they haven't changed enough to keep up the human situation.
Tom
ETA ~A big part of the reason that morality isn't keeping up is the religious/spiritual belief that ancient people were somehow more moral and closer to God than modern people. I see no reason to believe that. In fact, I think it's a big part of the moral crisis mentioned in the OP.~