I worked in SEO for 6 years, from 2014 to 2020. I had a network of about 20 sites doing a little over 1M monthly visitors. During this time I religiously tracked search traffic and page rankings with a cumulative volume of about 150M. IMO, the biggest contributor to the decline in site quality is both SEO spam and the tools that google implemented to combat SEO spam.

When I first started the low hanging fruit was these so-called long tail keywords. long, low traffic search terms that represent a specific question within a broader topic.

"how to invert a binary tree with recursion in python" would be a long-tail of "how to invert a binary tree".

A fairly small blog could rank for these lower-volume keywords without much work or investment. during this time, a low quality spam blog would have a large collection of barely-releated articles targeting very specific searches. Their site structure would be something like:

computerlinuxhow2guide.net:
- how to invert a binary tree in python
- how to quit vim on arch linux
- how to make an open world free-to-play video game in fortran
- how to install docker on ubuntu 18.04
- how to build a flappy bird clone in react native for samsung phones

Webmasters looking to build a more sustainable business would snipe a few longtails when possible, but their overall content would be topical and more cohesive.

datastructureslut.com:
- queues
- build a queue using an array
- build a queue using a linked list
- binary trees
- when to use a binary tree
- how to invert a binary tree
etc..

Google started to pages from sites with a lot of topical relevancy. Covering all the most popular search terms and interlinking these pages would give you a big boost. Affiliate bloggers responded by creating sites like "fishtankexpert.com" and "lawnmowerguru.com".

There are a LOT of these sites. Case in point: the examples above are just the first two things I thought of for $product $authority. and they both exist.

It became more common for larger sites to incorporate longtails into existing articles. Instead of writing a separate article, "how to invert a binary tree in python" could just be a subheading in a larger article. Tools like surferSEO became popular, before long it was common to see 10,000 word articles that covered thousands of search terms.

6 years ago, it'd be pretty common to find a forum about fishkeeping or a personal blog about landscaping on the first page of the search results for these kinds of keywords. But even then a lot of these sites would be abandoned or out of date. That made them an easy target for new webmasters to outrank, even with a limited budget.

The last major factor is profitability. With top 10 style articles, broad searches such as "best fish tanks" would bring in less sophisticated users. We'd often see purchases come in immediately after clicking on an ad. Most sales were one of the top 3 items on our list. Most visitors would skim the headlines, or read the top 1/3rd of the article.

specific Terms like "55 gallon saltwater fishtank" would bring in users who spent more time on your site, were more likely to read multiple articles, and more likely to return to our site at a later date. Overall, longtail traffic was more likely to make a purchase, and they would spend more money. Those sales often came in a day or two later, while broad traffic tended to purchase immediately.

Google never seemed to like longtail traffic. Not only because their pagerank algorithm was easier to manipulate, but also because they were less profitable for ad sales.

When customers could bid on highly targeted search terms that would reduce the number of people bidding on terms with low commercial value. In fact, if you set up an adwords campaign today you won't even be able to see traffic stats for these terms. They are obfuscated until you meet a certain spending threshold.

If you do optimize your bidding to avoid irrelevant searches, you'll get big warnings on your dashboard about "errors" they can "fix" for you so you don't "miss out" on all this "great traffic".

Since niche specific forums or blogs were basically dead, and these terms were almost entirely dominated by SEO spam, and larger "trusted" sites had started covering longtails in their broad content, google started to group topics and redirect searches to larger, more popular results.

The upside is that spam articles like "how to change the tire on a 1994 corolla" wouldn't easily outrank an article that has more general information about tire changing. There will be many popular articles targeting "how to change a tire", and "1994 corolla" is probably not mentioned on any of them. So google will assume that the uncommon portion is irrelevant.

When you have an error code, this strategy falls apart. The most common keywords in that search will be used in many different errors, while the portion specific to your error may only have a few results.

While there is still a lot of spam, these are not the low effort traffic grabs from a few years ago. These are sites that have invested heavily in content, back-links, and behavioral optimization. they'll be acceptable to a good chunk of the people that visit, and their advertisers will be more closely aligned with the results.

who needs search results anyway. If your question can't be answered by an advertiser or the knowledge graph (https://www.google.com/search/howsearchworks/features/) then it's probably not worth knowing.