Nature abhors a vacuum, and rabble always fill the vacuum. But why is there a vacuum? Where is everybody? Why is there a vacuum?
Several factors, not the least of which is media and cultural brainwashing.
When the courts started destroying the normal Christian doctrines in place in our society, this began to normalize apathy to Christian teachings and principles.
The media people also promote anti-Christian ideas and doctrines.
There are also a lot more things for people to do, and so many have dropped out of attending church services. The attendance of church was a social occasion and in the absence of more interesting things to do, many people preferred meeting like minded people in church.
There are a lot of factors regarding how we got here. I only named few.
The bigger question is "What can be done about it? "