You do realise that plenty of women also don't want kids?
There are huge downsides - it is expensive, there is a lot of boring dull grunt work involved (changing nappies, feeding, washing, dressing, as they age taking them to school, collecting, ferrying to clubs,events parties), the stress of worry (physical safety, bully, social media), risk of children having special needs and the stresses that places on a family including siblings and so on.
Physically childbirth can take a huge toll on a woman - prolapses, episiotomies, caesarian is major surgery, post natal depression are just a snapshot.
The best bits of having children - the joy of a happy family, being able to offer a child a good happy secure home and raise a morally decent educated person who contributes to society, and later as an adult having a deeply loving friendship and support as you age - are NEVER guaranteed. Plenty of kids turn out vile, not always the parents fault, drug problems, fall in with a bad crowd and so on. Economic migration means they may get a job miles away or even in another county. Plenty of kids grow away from their parents.
The main reasons are subconscious I think and three fold - a desire to propagate your genes and leave a legacy; something to do to give meaning and focus to a life (for many people who have boring jobs, low income, low hopes - children can overcome that and give meaning); and the hope there will be support in old age. You could add to that for some a desire to 'join the club' of 'normal' family life - succumbing to cultural pressure.
I know plenty of women who never wanted children, plenty who fluctuated at different times in life, and women who from puberty it was all they wanted.
People vary but it is no surprise really birth rates are falling as more and more women become economically independent, don't need the financial or emotional security of a marriage and see the downsides of childbirth and child rearing.