>>> I just understand what these people hope to gain by posting all those
^^^ Assuming that there should be a "don't" in that sentence . . .
The people who pay the spammers (at a fraction of a cent per link posted) couldn't care less whether or not anyone here ever clicks on the links. They simply know that Google ranks its search results largely upon the number of links to different sites that it can find across the internet. So, for example, someone searching for a particular news item will probably find sites such as the BBC at the top of Google's search results, simply because many thousands of websites (including this one) frequently include links to the BBC website.
Similarly, if the internet is full of links to SuperDuperKeto.com, anyone searching for 'keto' will find that website near to the top of Google's search rankings.