See now, that last statement is the core issue that is one of the biggest issues within the family court system.
1) Most children are not best placed to remain with the resident parent. In fact, ensuring that a child has regular lengthy contact with both parents is actually the model that has consistently, time after time proven to be what is best. That is that the child actually gets to "know" their non-resident/absent/parent without care.
2) 96% of applications made to family court are by fathers, mothers account for less than 3%. I doubt evidence exists to support my statement: mothers are more likely to be granted contact, sooner and for more lengthy periods. From my own assistance being provided to parents, overwhelmingly it is men. Two cases I've helped mothers and both on both instances were awarded and agreed the contact they were asking on the very first hearing. Compare that with the battle lines that I've helped some people with... not to mention my own.
3) The best interests of the child? There is a wealth of evidence that speaks against many decisions being in the best interests and decisions made by some Judges amounts to criminal decisions. For example, a Judge flipping a coin to see if a parent would see his 3 daughters or not (this actually happened)
Collusion, institutional sexism is another such issue.
Why don't we have a system where the status quo upon separation is abolished. 50/50 becomes a starting point. With this one implementation alone, you would prevent the need for tens of thousands of cases each year.
I have many ideas in my head how the "Family" court could be revolutionised for the better, not the worst. The system is adversarial and it is gender biased from before the child is even born.
While your statement might seem logical and right, I can assure you its that type of sentiment that has the family court as one solicitor said to me "completely and utterly failing the children"