Theological illiteracy among Catholics can be blamed, at least in part, on the culture of paternalism within the Church. The hierarchy still supports a top-down method of pedagogy, even for adults. (Even the word "pedagogy" implies a model of learning suited to children.) If that's the system one is formed in, it doesn't make for robust adult faith but, rather, theological dependency. 

As for Scriptural illiteracy, until the mid-20th century, Catholics were discouraged from individual reading of the Bible. The idea was that the laity weren't equipped to understand Scripture without the help of the clergy, and that our time to be nourished with The Word of God was during the homily at Mass. The Church still holds that homiletics is the primary mode of Scriptural catechesis for adults. The problem is that too little emphasis is placed in seminary formation on good homiletics, and it shows.

Jesus played with the children and taught the adults. We do it the other way around.