The reason is that JSP is not a traditional programming language. Learning the basics of JSP can be achieved with as little as a week's worth of training. Being a successful JSP programmer, however, requires that you learn many other skills. Keep in mind, however, that many of the required skills are simple to learn. The difficult task is trying to learn them all at the same time.
Most people make the mistake trying to learn everything at once.
Then in Part II of this series a logical order of learning JSP is presented. Organize a JSP project using several programmers where each is responsible for learning only a few skill sets at a time. By doing so, each person on the project team learns at a reasonable pace. Then, with time, rotate each person through a new skill set. This means a project can move forward at a acceptable pace and everyone gets to learn the skills.