Because life is good. IMO life is much better than non-life. My parents were poor and had a half dozen kids. Had I been my parents I would have stopped at 2 because they would not have struggled financially as much as they did by having 6. But had they stopped at 2, I would not have been born and I hate for me to not have been born; considering what my life has become. All of my siblings as well as myself are much more financially successful than my parents were and if you ask any of them, they are happy they were born rather than not born because my parents quit having children before they were born.
So you ask why should my parents have had children? Because now that we are born, we are happy they did, and so are my parents.
I am done, honestly.
I just let you read passage from Medea, by Euripides written 2400 years ago.
Greeks wisdom
Often, before this present time,
I’ve had to make more complex arguments
and struggled with issues more serious
than those which women ought to wrestle with.
But we, too, have an artistic Muse
who lives among us to teach us wisdom.
But not all of us—the group of females
who can learn anything from her is small—
in a crowd of women you might find one.
So I can claim that among human beings
those who have no experience of children,
who have never given birth to offspring,
such people have far more happiness
than those who have been parents.
With those who have no children,
because they never come to see
whether their children grow up
to be a blessing or a curse to men,
their failure to have offspring
shields them from many grievances.
But those who in their own homes
have a sweet race of children growing,
I see them worn down with cares
their whole life long. First,
how they can raise their children well.
Next, how they can leave their sons
sufficient livelihood. And then,
it’s by no means clear that all the work
produces good or useless children.
There’s one final problem,
the worst for any mortal human being—
I’ll tell you: suppose those parents
have found a satisfactory way of life
and seen their children grow
into strong, young, virtuous men,
if Fate so wills it, Death arrives,
and carries the children’s bodies
away to Hades.
What profit, then,
is there for us and our love of sons,
if the gods inflict on mortal men,
in addition to their other troubles,
this most painful further sorrow.