No special training is needed. I have never heard of anyone complaining because their youth leader or Sunday School teacher did not have formal education in theology and ministry. Ministry is something that all Christians have been called to do, regardless of their educational background. I don't hear that either. Yet, look at the ineffectiveness of average Christian Education programs, which typically produce a preposterous amount of biblical ineptitude.
Preparation is often a consumer of too much time.
Valuable time is wasted that could be spent actually doing ministry instead of just talking about it. We are all given a very brief time upon this earth, and it is a constant struggle to determine the most appropriate way to make the most of this time, and to honor our Heavenly Father. We don't want to waste it. Yes, there are some. But maybe the school or the student or some other circumstance is to blame, rather than the notion of education.