Not reading the Bible enough is far from something that is restricted to youth. Far to often adults have the same issue. The Bible in many churches is reduced to a tool teachers use to back their points. Far to few churches teach the basics of how to read/study God's word, how to learn what it means and unlock its mysteries in your personal studies.
Much of church teaching has been turned into a teacher or preacher giving scripture context then preaching on it for a period of time. Members go home and file the scriptures away but do no amount of study on them to confirm/deny the teaching they received. This is ironic since you retain very little of what you hear in a sermon or class without outside reinforcement. In my Bible school days they taught us that about only 10 percent of what you hear you actually retain. And there is some truth to that. Largely it depends on what the person does during the teaching, (i.e. sitting idly, taking notes, jotting personal thoughts and extra scriptures to look up).
In truth the issue isn't something you can bring back to a single person, it largely is all our faults to some degree. Children aren't trained properly by parents, parents aren't trained properly by their parents/mentors/those who led them to Christ. Setting fault isn't really the issue, the issue is how can you fix it?
It is a shame but I know many people that still say that the bible confuses them, they don't know how to study it and just reading it isn't productive (to some degree this is do to the wandering mind effect that takes place when you read something your heart just isn't in). I've found that when you teach people how to ask the questions they need, how to use tools like the multitude of free study software and websites, that they begin to enjoy it more. When I've taught or preached Sunday services in the past I've always taught from a standpoint of bringing someone to a Biblical conclusions on their own. Ask questions, lead them from those questions, help them understand your scriptures, and help them walk into the message themselves rather then just giving a three point sermon on a topic that relies heavily on repetition, gimmicks, and animation to keep interest. After awhile people begin to ask those questions themselves, they begin to do it in their own time and it opens a brand new avenue for study of God's word.
It's a shame but if more preachers just went out and showed people how to study God's word on their own and use free tools like GPL versions of study software, and other free very good study programs and websites for in depth study then things would begin to turn around and we'd see a huge increase in God's outpouring in churches.