The difference is that the cost to give your kids what you had as a kid and the opportunities you later had access to has gone up. People don't want to raise kids if they can't give them a life at least as good as they had.

Yes, there's lots of things about today that are better than 30 years ago. TVs are bigger, cars are safer, etc. But the ability to give you kids the childhood and initial opportunities you had seems far less likely to many people.