The historam reflects the dependence of the number of sites on their quality.
The quality of sites decreases from left to right.
Sites were chosen according to the subject defined by the keyword:

As well as belonging to a particular domain zone

Despite the fact that there are hundreds of millions of websites on the Internet, the best of them are thousands.
These are several thousand sites worthy of attention on various subjects - from news and portals to online dating fit in the given graphs. The rest for you seems to be just a click away - in Google, the output is infinite, but at the same time it eludes, because it is impossible to physically study and learn the entire Internet. For one life, for sure.
Domain search engine
HREF just selects the results of the most reliable, expert, quoted - "best" sites, avoiding unnecessary-left links.