An seo company will buy a bunch of recently expiring domains related to a specific topic, and do it in a way that hides who the owners are. They build blogs on these sites, and fill them with the lowest grade content. I've see stuff that's "spun" (plagiarized content where a percentage of words have been replaced with synonyms, so that it appears original) and other stuff that's farmed out to writers in developing countries who work for pennies (A lot of articles with no real substance, written in poor english.)
The owner then links all the blogs to each other, so they appear to have domain authority. Then they sell back links to their customers. This fools Google into thinking your website is trustworthy (because everyone is linking to it) and you get better placement in search results.
In short, its a way anyone can buy popularity online.
My old job was in advertising. Some of what I produced actually informed consumers about new products. But most it was vanity projects. One example: A chiropractor paid for a billboard with him standing next to a million dollar therapy machine, despite the fact that no potential customers would understand what the machine was. He just wanted to show his competitor that he could afford a shinier new toy. Since most of the treatments he offered were medically dubious, it would have still been bullshit even if we made an effective billboard.
Believe it or not, most of our projects were like this - the result of someone's vanity or stupidity. But even the good work we did, most of it just part of some companies advertising arm's race with their competitors. If the entire ad industry collapsed tomorrow, the only thing we would notice was the lack of junk mail littering our mailbox.
I'm happier in my new job, though it's no less bullshit. I run a social media product that doesn't have a measurable impact for 95% of my clients. In truth, they don't need social media in their industry. But they've been told "everyone has to be on Facebook nowadays" and that's how I make a living.
https://www.amazon.com/How-Good-bye-Depression-Constrict-Eve...