Children not "central to marriage" according to Pew Research Center; but why are they so often central to divorce?

A quick browse of Pew Research Center excerpts just now left me with this statement “children are not central to marriage but are often central to adult happiness and fullfillment.”  That may explain why there are often such bitter custody battles when couples divorce. Sure, the cynic in us would like to say it’s all about the money. But many times, it just comes down to the fact that folks just love their kids and both parents want to keep the children  for the fullfillment children bring and the sense of happiness they bestow, notwithstanding how expensive they are; and that is why couples tend to fight so viciously over their kids sometimes and why children are often so central to a divorce action. It’s all very sweet when you get right down to it.