There are good guys and bad guys in old westerns and the bad guys wore the “black hats”.
The web is still a frontier, and hopefully will always be one(but that is another subject!), and there will always be bad guys trying to rustler someone else’s cattle.
The worst bad guys steel passwords and give your computer viruses etc, but there are blackhats in every corner.
See the post on how SEO works to understand the ‘hows’ but the “Why” is easy: they are just trying to make money.
Quick Buck-artists Ruin your search results!
The Black-Hats use key-words described in the SEO Arms-Race article to make the Search engines think that they are really really focused on the subject you’re looking for with the words in your search.
SEO tactics of loading a web page with words on a subject aren’t always evil, but two things happen far too frequently
1) Black-Hat developers use programs to scrape paragraphs on info from public sites (or steal it from private ones) and don’t add anything new to the web
2) These computer generated sites are usually more ads than content, and are known to use some of the least scrupulous ad companies (with aggressive tracking cookies or worse) as the reputable ad companies wouldn’t allow their ads on these sites.
3) Search gets worse: A little independent person making a site talking about their hobby will likely use far fewer “keywords” and show up less. Worse still, because the “blackhat” sites scrape(steal) other peoples content, the little guys words might appear on the bad guys site, then the search companies suspect the good guys of being bad guys.
See “Throwing the baby out with the bathwater”
Results are you can’t find many small but expert content sites.