Interesting that 5 years ago is exactly when this page showed up according to the Wayback Machine: https://docs.github.com/en/get-started/exploring-projects-on...

In it they explicitly call it out as a ranking metric

> Many of GitHub's repository rankings depend on the number of stars a repository has. In addition, Explore GitHub shows popular repositories based on the number of stars they have.

Yet another case of metric -> target -> useless metric