[detaro]

I'd guess it's related to how ambiguous a "star" is, and people use them for very different purposes, a common issue with sites that do not have distinct options but only "star"/"like"/....

E.g. I treat stars as bookmarks: I star everything I come across that seems somewhat related to my interests, but isn't relevant right now. In the vast majority of cases, I at best have skimmed the readme. If I'm looking deeply into something, I might even be more likely to not star it.

This conflation of purposes means a lot of noise in the signal you can get out of it. It's some kind of popularity metric, but not a clearly defined one.