We simply have no time for Him. We are not irreligious. We're just busy. And we are tired. Other matters are pressing and heaven can always wait.
Preoccupation is certainly the arch enemy of spiritual growth and Christian service.
We cannot attend a church school class or a service of worship because Sunday is the only day when we can catch up on our sleep, or mow the lawn, or play tennis, or visit relatives. We really mean to cultivate a right relationship with God, but somehow there never seems to be enough time.