That's mostly a factor of lower childbirth rates. Put plain and simple: people used to have 3+ kids (or more, if you counted those who died before age 6), so if one or two died, got severely injured, turned mad, criminal or celibate-religious there would be still at least one or two other kids to inherit whatever wealth the family had (i.e. usually the farm or trade shop) and pass on the family name.

Nowadays middle-class people tend to have just one or two children, they literally cannot afford the space or childrearing costs for more - for lower classes eligible for government assistance such as the un(der)employed the situation does look different as society picks up large parts of the tab. Additionally, ever rising requirements in employment criteria make it necessary to invest more and more into their education: up until maybe 2-3 decades ago, even a school dropout could work in construction, a factory, retail, farm or mine and make a relatively decent living. But these jobs have largely gone away to China/India or to automation, so the few employment options for "undereducated" people are highly contested.

And so, the kid must turn out perfect: there is no room for the kid to make mistakes, especially not ones that endanger their career prospects, and hence all the helicopter parenting.

On top of all of that come decades of media/politician "fear brainwashings" (aka, the "pedo child-snatcher van" myth), as well as the legitimate collapse of a high-trust society (homeless, drunk and mentally ill people literally everywhere in major cities; police simply not enforcing laws any more).