While it's normal for childfree people to be asked why they don't want kids, asking a parent why they want or have kids can be seen as taboo. I’ve taken the liberty of identifying a few reasons why I think people want or have kids. 

1. Their family life growing up was amazing and they want to re-create it

2. Their family life growing up wasn’t amazing and they want a do-over

3. They meet someone who makes them want kids

4. They want to feel unconditional love without having to earn it

5. They want to feel needed

6. They want to be a better person and need a forcing mechanism

7. They are bored

8. Everyone around them is having kids

9. They are terrified of being alone or dying alone

10. They crave purpose and legacy

11. They think they will regret not having kids

12. It’s the only lifestyle choice they have ever considered