Firstly, "Computer Chess" in SEO terminology is a single keyword.
But it is a keyword which reveals very little about the user's intentions.
Google has changed it's algorithm a lot since the days when "keyword stuffers" could just throw a bunch of keywords in their <head> section and dominate the rankings.
Intention
These days Google looks for INTENTION and those two words could mean anything.
For this reason, it's much wiser to use so-called "long tail keywords" which contain more words than 2.
For example: "Best Positional Chess Engine" is a very specific keyword which makes the searcher's keywords absolutely clear.
And guess who is at number 1 ranking?
Semantic Keywords
Google also ranks pages which not only have the keywords but have semantic keywords within the articles. This basically means phrases that its algorithm has spotted on similar pages and so are consistent with such content.
So using our first example of "Best Positional Chess Engine" - Google might also look for phrases such as "knight outpost" or "pawn structure" etc inside the post, as part of its ranking process.
Again, this prevents keyword stuffers from gaming the system.
There are a lot of other ranking factors, but PA or "page authority" is only one, so based on the vagueness of the term "computer chess" (in the eyes of Google) and probably the lack of keywords (semantic and otherwise), some pages which we think should rank, do not rank.
SEO is a complicated, but worthwhile to learn if you want organic traffic on your site.
