Maybe the author moved on because he wanted something more then effectiveness - fulfillment. I see many practitioners get so caught up in what they can do with magick, they forget what they should do with magick. Making stuff happen is useful and fun, but it's most powerful when paired alongside reflection and discovery of the divine within yourself and the world around you. For many, magick becomes food for the ego instead of a means for self-improvement: they keep wanting bigger spells and bigger results, and forget about balance.
Of course, it could be many things, but that is at least one idea that makes sense why someone would move on from an "effective" system. That, or boredom....