It is somehow sad that "caring about content quality" is considered SEO and not just making a good website.
I think more than half the things you mentioned are only good SEO because search engines want to send people to websites they will like reading. I think when that is the case, we should be crediting people for making good websites, not good SEO.
Yeah, looking at it from a purely SEO perspective always makes decisions look kinda shady, as in they're trying to game some algorithm in order to gain more exposure. Wikipedia's biggest SEO factor has to be the massive amount of backlinks it gets. Those are purely organic and happen simply because it is generally the best authority on most any topic. It's more of a testament to how genuinely good Google's algorithm has become rather than some masterplan by Wikipedia.
Once you have 150 million inbound links, the strategy choices are easy - focus on content quality! But you have to remember what Day 1 was looking like: a tiny community, no inbound links, and a fair amount of other encyclopedia competitors trying to attract authors. Now the strategy choices are quite interesting - at the beginning of a startup you have just enough energy/runway to "kill it" in one area. Which one do you focus on? Generating the world's best content alone without the heavy lifting they've done on deep interlinking and other SEO-friendly moves wouldn't have cut it.
Further down in the comments you'll find a research paper [1] that analyzed why Wikipedia succeeded where others failed. I am not sure I bought into the conclusion (which prompted my initial comment), but at least it has a comprehensive listing of all the main players at the time:
Yes, I believe that Wikipedia and its authors never put much thought into SEO. They just think about how to best structure the information and make heavy use of links, which also happens to be a good strategy for SEO.
The Google search rank algorithms changed a lot more than the overall structure of a good Wikipedia article in the last 20 years.
Have you ever encountered on Wikipedia a sentence like this:
"...because a <a>blue</a> <a>whale</a> did..."
rather than
"...because a <a>blue whale</a> did..."
Obviously, the latter version would have been more useful, and I find it difficult to believe that a human being would have made such a mistake. Don't get me wrong - such instances are rare, but they do happen and are an indicator that not all links are generated manually. I don't know what they are using today (if anything), but as someone else pointed out, in the early days they used UseModWiki to ensure a high level of deep interlinking. We can argue that this was done to improve the UX, but the level of ambition that went into it signals that they also saw it as a strategic move (and they would have been right to assume that - 20 years ago, a highly interlinked site was likely the best bang for the buck in SEO when it came to how to prioritize your time and resources).
SEO changed dramatically over the last 20 years. Thankfully, we are today exactly at a point that you described (it all started with Panda in 2011). As you'll see below, getting there was not just a technological challenge, but also one of fixing misaligned incentives.
Prior to 2011, Google enjoyed a mutually beneficial relationship with content farms which splattered their pages with AdSense ads (and Google ranked them highly). Can you imagine how it must have sounded for the Panda engineers to pitch to Sergey and Larry that they wanted to replace all those highly monetized websites with Wikipedia?
Matt Cutts commented that "with Panda, Google took a big enough revenue hit via some partners that Google actually needed to disclose Panda as a material impact on an earnings call. But I believe it was the right decision to launch Panda, both for the long-term trust of our users and for a better ecosystem for publishers."
“Google Panda is a major change to Google's search results ranking algorithm that was first released in February 2011. The change aimed to lower the rank of "low-quality sites" or "thin sites", in particular "content farms", and return higher-quality sites near the top of the search results.”
Back in the early to mid 2000s, I learned web design/development by volunteering to create websites for charities/NGOs. In the process, I
* ensured that the code (HTML and CSS, only basic non-AJAX, JavaScript) was standards-compliant (at the time, XHTML [1] was “the big thing”)
* implemented basic usability guidelines as advocated by Jakob Nielsen [2] in his Alertbox newsletter and
* followed Mark Pilgrim’s suggestions in his Dive Into Accessibility
Carrying out the above and simply focussing on quality content was enough to rank highly in Google’s search engine results and I never had the need nor inclination to do any research into SEO. Back then the mantra in the web development books was that “content is king” – and Google reflected this philosophy. Sadly, the Web has changed a lot in the intervening years.
Equivalently, the challenge in running a search engine is to decrease the divergence between “what makes a website good” and “what makes us rank you higher”.
I think more than half the things you mentioned are only good SEO because search engines want to send people to websites they will like reading. I think when that is the case, we should be crediting people for making good websites, not good SEO.