And yet there are literally innumerable mature adults who have no religion and moreover no need for one. How come?
Unless of course you're going to define them as not mature and not adults?
It may be that those who have no religion simply haven't "discovered" it.
... which is not going to apply to those who have had it (or had one) and lost or abandoned it.
And of course, there are many reasons why some distance themselves from religion; though the majority in the world express at least some affinity with it.
The issue there becomes one of differentiating between actual, sincere believers (true believers, without any disparaging overtones in that phrase) and those purely nominal cultural adherents.
Well, there we are in the realms of the unprovable, if I can put it that way. There are, I believe, though it's unprovable, huge numbers who you might describe as nominal, cultural, adherents, who, when push comes to shove, would be sincere believers.