If you read some of the synopsis at the bottom it explains it. It's a mix of laws and societal attitudes.
This data is also further simplified:
> The percentages in the study reflect cases in which both parents want custody and no complicating circumstances exist ― such as criminal convictions or long-distance separation. It demonstrates the most commonly awarded visitation schedules given to a noncustodial parent by state.
This data is also further simplified:
> The percentages in the study reflect cases in which both parents want custody and no complicating circumstances exist ― such as criminal convictions or long-distance separation. It demonstrates the most commonly awarded visitation schedules given to a noncustodial parent by state.