The primary reason and purpose is to educate, train and raise our children in the Catholic Faith as handed down to us. We are the first and foremost Educators of our children. We have been given a great privilege and obligation to raise our children in the ways of God - preparing them ultimately for an eternity in heaven with God. The secular education is secondary and finally outside activities, group organizations and lay religious groups are options, time permitting. Many times parents feel pressured by the demands of everyday life to turn over this God-given right to others that are pressuring them.
Most parents are still in the mindset of public schooling.
This aspect of socialization is abnormal. It creates a situation that is artificial and eventually demoralizing. This includes joining organizations, secular or lay religious. The need here is to teach your children at home. Time permitting, outside activities can be fun.