Some documentation is sadly lacking generally, but even some very good documentation in terms of detail is not terribly useful to a beginner as it is often more a reference work for people with some experience.

With a bit of experience a detailed reference is great, but it can completely overwhelm a beginner who is better served by being given some simple worked examples of a core sub-set of features/methods/properties/processes/… then being given the more referencey docs to find the other details (ideally with some starting pointers, linking what they were shown in the tutorial examples to relevant bits of documentation).

Remember when 4X games came with paper reference manuals? If you skip the SMAC tutorial and go through the reference in order you'll hit the copter and hovertank units (late-game additions that you don't need to care about initially) long before the speeder (something you have access to early on, from the start in the case of one player faction). Just giving beginners reference docs is much the same thing.

Many have become attuned to searching for a tutorial elsewhere, assuming the docs will be overwhelming initially, even if more introductory information is available for a given thing. Also, many or introduced to new libraries and such through tech blogs, another reason for that being their starting point. And of course if searching via Google et. al. you have the issue of blog-spam that is SEOed to the nth degree coming up before the better documentation.