Well, that handholding can be a lot. And, there's also a question of the background the reader has at their disposal.
An analogy: If you go to college, Physics 101/102 is taught without assuming the student knows calculus (because they are typically taking Calculus 101/102 in that same semester).
Physics 301/302 often covers the same topics, but expecting the student knows calculus, linear algebra, and differential equations. A person on the street can typically understand the textbook for Physics 101. The book for 301 is incomprehensible without the math background.
The 101 level course can be seen as telling you, in not much over layman's terms, what is happening. The 301 level course gets into the fundamentals of why it happens, and gives you tools to handle far more complex scenarios.
Edit to add: So, to bring that around to gaming - a beginning worldbuilder's book would probably be "here's a bunch of stuff you could consider doing". A book for a 20-year worldbuilding veteran might be more like, "How to make publishing quality worlds"...