Some people wander from the faith because they are selfish. They want to get something out of it for themselves, so they get bored while serving God and prefer to serve themselves. Some people leave the Church because they were treated poorly by someone that should have treated them with the same grace and love that Jesus demonstrated. Some people are led away by falsehood. Someone tells them something that isn’t true about Jesus or the Church or the Bible. It’s always good to look into suspicious claims before adopting them as truth.