Why are seemingly important topics not covered in textbooks?

An important distinction that needs to be considered, in the design of any course, is the timescale over which the knowledge is expected to be applied.

• At one end of the spectrum are courses where the knowledge is expected to become obsolete only on a time scale of centuries, such as calculus or Newtonian physics (yes, they change: try reading a calculus text from 100 years ago and the notation is likely to be somewhat confusing), but are generally about fundamental knowledge and core principles and thus often rather removed from immediate applicability.
• At the other end of the spectrum are courses where the knowledge is immediately applicable, but where it may become obsolete quite quickly, such as training in particular software systems or laboratory equipment.

Institutions then tend to organize themselves along this spectrum according to their goals:

• Strong universities tend to focus much more on the long-term end of the spectrum, because they are trying to give their students skills to last a life-time, and indeed to help those students become the ones who create new systems and applications that render the shorter-term knowledge obsolete.

• Vocational schools tend to have a mix that aims to give the students both immediately applicable skills but also enough foundations that they won't need major significant retraining for a number of years.

• Professional development and other "on the job" training tends to be much shorter and focuses on the short-term skills that are needed now and where it's OK if you need to train again on the new system in six months.

Now, let's consider your example of search engine optimization: this is a rapidly moving target, since it's based on adapting to the current methods that the current search providers happen to be providing how the internet happens to be organized right now. Cutting edge SEO techniques are being invented and destroyed constantly. Pretty much any SEO technique from five years ago is totally useless today, and SEO didn't really even exist as a field ten years ago.

As such, you should expect a marketing textbook or course at a good university to pay little attention to SEO, but instead to focus on more foundational principles. On the other hand, if you search for SEO textbooks and courses online, you'll find a lot of more vocational or corporate resources available.

In short: educational resources adapt to the timespan over which they are intended to apply. The longer a timespan an education is intended to cover, the less it will focus on "hot topics," and a good undergraduate degree is intended to last your whole life.

I am going to offer a bit of a diverging view here. In his answer, Jake offers the explanation that SEO is just too much of a "moving target" to be of value as a university course. I strongly disagree. Just because a topic isn't "static" does not mean that you can't have good, university-level courses on it. A prime example of this is security, specifically malware detection: the entire field is basically an ongoing race between people finding ways to detect malware, and others finding ways to prevent detection. The state-of-the-art tools change literally every month. By the time you even know about a given concrete threat, it's probably already not the most dangerous thing out there anymore. However, clearly there is method to the madness - there are principles and techniques that can be taught, which remain useful for a long time even if the concrete tools change. In the case of malware detection, this would be knowing about honey pots and sandboxing (to find and analyze real malware), malware signatures (both exact and fuzzy), heuristic methods, behavior-based methods, and so on.

For SEO, the same thing holds true. In a nutshell, SEO is a race between search engine makers wanting to show the best content to its users, and "optimizers" trying to figure out ways to trick the search engine into thinking that their mediocre stuff is the most relevant content to a given search query. How you do this concretely changes all the time, but the fundamentals have, to the best of my knowledge, remained relatively stable.

So, why is SEO then not routinely taught in marketing?

Likely, because for understanding how SEO actually works "under the hood" you should have:

• Reasonably advanced knowledge about mathematical graphs and algorithms on graphs
• Knowledge about the theory of recommender systems
• At least basic knowledge about computational linguistics
• And of course you should know how crawling and indexing actually works on Web-scale

All of these are not topics typically taught to marketing students. That is, in order to properly teach SEO (basically a computer science topic, after all) you would need to go onto a pretty significant tangent. If you don't, you will end up teaching a course that boils down to "you have to use these kinds of words using these frequency in these tags" without giving students a chance to understand why, and then you are back to Jake's answer.

(but yes, many computer science degrees, especially those with a focus on information retrieval, actually do teach SEO or a variant of it)

To put it simply, I think what you're facing is the difference between the purpose of courses that contribute to a university degree, the practical needs of companies that hire, and the desire of search engine companies to erect barriers to engineered SEO.

To restructure what you're asking, companies want SEO experts to help raise their online profiles (relative to the online profiles of similar competitors). Google, Bing, Baidu, etc. want to rank sites based on quality of content and ease of parsing pages rather than give into these SEO machinations.

It's hard to see how a university course could really help here. It could begin with a cursory and theoretical account of what SEO is and what it seeks to accomplish, but this would tell you little more than you can learn from a day of sleuthing about on the Internet.

After that, the problem is that Google, etc. won't tell you specifically what you need to do to accomplish SEO. Thus, there's a bit of a dark art of guessing and figuring out how to manipulate pages to raise the profile of a site. How does one construct a university course around industry secrets relative to companies that don't want people to know the exact means of optimizing?

It would seem you would need someone in the industry rather than a CS or marketing professor to teach it. But anyone who can do it well enough is gainfully employed and employed specifically to use that skill for their employer. The precise methods are changing so fast that the techniques I used in 2011 were outdated (meaning no longer provided an advantage) the last time I looked at in 2013.

To give an analogy, it's roughly like offering a course in contemporary street art where contemporary means -- drawn during the semester the course is taught. Sure, we can talk about in the classroom, but the experts are mostly criminals so how we do get access to fresh work and understand it?