Why do people choose not to have them? Personal decision one makes...

To have decendants and pass the name, customs, family history on, and to have your own child to love and cherish.

I guess they have their personal reasons but I never wanted any kids and never had any.

Because they can.

1: repopulate
2: your child gives you the option to put another good person in this dark world

The fundamental reason why we exist.

To keep the species going.

because he can not have a dog😄

Taxes

To build families and pass down their genes.