In 2016 a Pew Research Center survey received the following reasons Christians abandoned their faith:
Learning about evolution when I went away to college.
Religion is the opiate of the people.
Rational thought makes religion go out the window.
Lack of any sort of scientific or specific evidence of a Creator.
I just realized somewhere along the line that I didn’t really believe it.
I’m doing a lot more learning, studying and kind of making decisions myself rather than listening to someone else.
“And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled in the body of His flesh through death, to present you holy, and blameless, and irreproachable in His sight – if indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel which you heard, which was preached to every creature under heaven, of which I, Paul, became a minister.” Colossians 1:21-23.