Because its a necessary logical consequence of atheism. You MUST believe it because it’s part of the baggage that you accept with the atheistic worldview. To deny it is to be logically inconsistent (and thus self-refuting).
Atheism is a concept, a metaphysic (means of explanation, organizing principle) and a worldview. Your personal opinions on various matters don’t change the facts about what atheism is. So, rather than discuss your personal life (for example, you’d have to tell us of all your moral failings and every time you didn’t tell the truth, etc.) it’s best to discuss the philosophical concept of atheism. So, it’s “atheism” not “Leela the atheist” which is being evaluated.
In the atheistic model, your family has no ultimate purpose – that’s a necessary corollary of the belief that there is no God, no immortality of the soul, no life after death, no judgement for human actions, and that human life is an accidental, unnecessary emergence from unintelligent, unconscious, blind physical laws.
There can be no ultimate purpose for human life if that life itself emerged from processes which themselves cannot confer ultimate purpose or meaning.
So again, your family is ultimately unnecessary and does not have an ultimate purpose or meaning.
Therefore, if you establish some kind of purpose for yourself in caring for something that has no ultimate purpose – this is what we’d call a trivial (and basically illogical) purpose.
Ultimately (in the end), there is no purpose, meaning or value to your activity of caring for a family (which is also unnecessary and lacking ultimate purpose – as you, yourself are).
This may help. Dr. William Provine is a most prominent atheistic scholars. His ideas here are non-controversial in the atheistic world – they follow logically and are necessarily a part of the atheistic worldview:
“Naturalistic evolution has clear consequences that Charles Darwin understood perfectly. 1) No gods worth having exist; 2) no life after death exists; 3) no ultimate foundation for ethics exists; 4)
no ultimate meaning in life exists; and 5) human free will is nonexistent.”
William Provine, Evolution: Free Will and Punishment and Meaning in Life, Second Annual Darwin Day Celebration Keynote Address, University of Tennessee, Knoxville, February 12, 1998 (abstract);
You may have heard of the atheist, Richard Dawkins. He summarizes atheistic philosophical thought in the very same way:
The universe we observe has precisely the properties we should expect if there is, at bottom,
no design, no purpose, no evil and no good, nothing but blind, pitiless indifference. As that unhappy poet A.E. Housman put it: ‘For Nature, heartless, witless Nature Will neither care nor know.’ DNA neither cares nor knows. DNA just is. And we dance to its music.
Richard Dawkins, River out of Eden : A Darwinian View of Life (London: Phoenix, 1995), 133.
Atheist Steven Weinberg:
“Worse, the worldview of science is rather chilling. Not only **do we not find any point to life **laid out for us in nature, no objective basis for our moral principles, no correspondence between what we think is the moral law and the laws of nature, of the sort imagined by philosophers from Anaximander and Plato to Emerson. We even learn that
the emotions that we most treasure, our love for our wives and husbands and children,
are made possible by chemical processes in our brains that are what they are as a result of natural selection acting on **chance mutations **over millions of years. And yet we must not sink into nihilism or stifle our emotions.” Steven Weinberg
nybooks.com/articles/21800
Atheist Jacques Monod makes this very clear and explains that there is a fundamental conflict between the atheistic metaphysical view (that there is no ultimate purpose) and the religious view:
… the scientific attitude implies what I call the postulate of objectivity—that is to say, the fundamental postulate that
there is no plan, that there is no intention in the universe. Now, this is basically incompatible with virtually all the religious or metaphysical systems whatever, all of which try to show that there is some sort of harmony between man and the universe and that man is a product—predictable if not indispensable—of the evolution of the universe.
— Jacques Monod, Quoted in John C. Hess, ‘French Nobel Biologist Says World Based On Chance’, New York Times (15 Mar 1971)
I can find many more like this if you’d like. Again, this is not controversial at all within the circles of atheistic thought. It’s the fundamental axiom of the atheistic view.