I don't believe that this is necessarily done intentionally by Christian parents. There are a lot of things that are taking up our time and the time of our children. School activities and life are busy. We want our kids involved in extracurricular activities to ensure healthy socialization and help them as they seek future opportunities. Most parents have been trained to think that going to church and being involved is enough, but with the continued move of our culture to being less and less tolerant of Christian teaching and faith.
I would posit like an acquaintance of mine, Richard Melheim, that one of the things that was initially created with the hope that it would help the Church, but has actually harmed her - Sunday School, namely Children's Sunday School. One need only look to the history of its formation to see how a once really good idea went further than ever intended and became more far reaching. Sunday School was initially developed to done with orphans in orphanages. Since, these children had no parent to raise them in the faith, the need to educate a child in the faith needed to be taken up by representatives of the Church. In the Twentieth Century, Sunday School became a staple in every congregation and, over time, parents began to utilize that tool as the primary source of Christian education for the home. Personally, I see positives of Sunday School and would not seek to remove it, but each congregation should seek to develop a method in which the children are given a ground work and the parents are equipped with the tools to continue developing their children in the faith throughout the week. The ultimate goal is to build up families in the faith, which is so important and, in doing so, will build resilient families that is equipped to weather the storms and struggles that all families face.