Keller et al. (2004) reported results from studying cultural parenting styles that indicated that

I believe the answer is:  parenting styles fit cultural expectations.
Most parents would designed their parenting stype in order to 'create' a children that they could boast off to their peers.
For example,in japanese culture, they expected their childten to be able to maintain high grades in high school. Because of this, the parenting stype of japanese parents tend to be really strict to make the children maintain their grades.