Why a Catechism Just for Catholic Adults?

An interesting question has been asked via our Facebook page called Louisville Why Catholic:  Why is there a separate Catechism today for adults in the U.S.?

The Apostolic Constitution, Fidei Depositum, by Pope John Paul II, prefaces the comprehensive Catechism of the Catholic Church (CCC) by stating:

"I ask all of the Church’s Pastors and the Christian faithful to receive this catechism in a spirit of communion and to use it assiduously in fulfilling their mission of proclaiming the faith and calling people to the Gospel life. This catechism is given to them that it may be a sure and authentic reference text for teaching catholic doctrine and particularly for preparing local catechisms  . . .

"This catechism (CCC) is not intended to replace the local catechisms duly approved by the ecclesiastical authorities, the diocesan Bishops and the Episcopal Conferences, especially if they have been approved by the Apostolic See. It is meant to encourage and assist in the writing of new local catechisms, which take into account various situations and cultures, while carefully preserving the unity of faith and fidelity to Catholic doctrine. The United States Catholic Conference of Bishops took several years to bring together a volume that is both shorter and more reader-friendly, than the original Catechism of the Catholic Church."