Stars on a Github repo are a reasonable proxy for engagement, even though they're point-in-time for a given user.

That is, users add a star and rarely remove it.

When a repo is useful, they tell their friends, and those new people come in, and some proportion will star it.

So the star rate is useful; if the repo has PMF and the rate of a new user starring it stays the same, then it will have ever-increasing number of stars.

This is all assuming the stars aren't bought, an increasingly poor assumption.

But even in that case, a compounding set of bought stars gets increasingly expensive to fake.