When we think "religion," we often think in terms of an institutional church, a denomination, or one of the world's great religions, i.e., Christianity, Judaism, Islam. Or we think of any number of other religions with their worship edifices, holy books, practices, and values. Some people do not adhere to or practice any of these religions.
But if we think "religious" instead of religion, and we recognize that religious means ideas, assumptions, attitudes, and values characterized by certain spiritual faith perspectives, then it is easier to understand that no human being is or ever has been religionless. All human beings make faith assumptions about the divine, the universe, life, death, purpose, and more. So while there may be secularizing or "desacralizing" trends labeled by sociologists as "secularization," these trends never yet have resulted in individual human beings becoming somehow religionless. Human beings are by virtue of creation, religious beings.