People can believe almost anything, and any number of incompatible things, for their whole lives - when they are 1. dishonest, and 2. have a short attention span. That's most people - including nearly all intellectuals.
But there are deeper factors at work in my opinion. One is that modern people are different (innately) than people in the past. We nearly all start-out with direct personal experience of the spiritual world as young chidlren, but quite soon become detached from it; and must consciously choose whether to believe in the reality God and the spiritual in general, and then perhaps choose further to believe on Jesus Christ.
For us modern adults (and indeed older children and adolescents) theistic belief is not spontaneous, nor unconscious - and cannot (under recent social conditions) be imposed on us.
This fits with the heart of Christianity, which has always been supposed to be a conscious and free choice - but the purity of that teaching became contaminated by its adoption as a state religion and means of societal control (maybe that was necessary in the past, but those days are gone forever).
On top of all this, I am compelled to acknowledge that there seem to be a much higher proportion of unrepentant sinners born now than ever before; I mean the mass of people who do not acknowledge that they are sinners.
Most modern people are, in effect, psychopaths - whose basic set-up is evil.
Clearly that is encouraged from the top-down by the global, national and other leadership; but it could not be so widely and comprehesively be imposed (without any backlash) unless most people were pretty much that way inclined already.
Thus we live in the most sinful times ever known - sin being the state of turned-away-from God; working against God, The Good and Creation. So much so that the reality of God, creation, goodness and sin are all denied - and people are utterly unaware of their denial, and deny this fact - although in principle all-this can be known by anyone.
Christians are - and this is much more obvious now than six months ago - in a tiny and shrinking minority; and have been betrayed by the leadership of all the major churches.
The prospects of any institutional revival of Christianity are worse now than at any time since the day of the crucifixion.
This is our situation, and it would be good to get used to it; and work from where we actually are.