Many reasons. A few that come to mind:

-Desire to travel (or accomplish whatever their retirement plans are) before they are too old. -Just like we don't really know how to parent, they don't know how to parent. -Parenting has become polarized with (mis-)information overload manifesting in disagreement between parents and grandparents. -...

Interesting about the retirement thing.

I think most parents know how to parent and teach better than they'd realize. Parents are so disempowered. They are shoved out of education and told they can't teach because they are not trained teachers.

They are constantly judged and told how to parent then others, so they no longer trust themselves and their instincts.

Sad about the arguments around how to parent caused by misinformation or information overload.