This is kind of fascinating and seems worthy of more detailed study. I'm sure almost anything looks stable compared to javascript/python ecosystems, but would be interesting to see how other ecosystems with venerable old web-frameworks or solid old compression libraries compare. But on further reflection.. language metrics like "popularity" are also in danger of just quantifying the churn that it takes to keep working stuff working. You can't even measure strictly new projects and hope that helps, because new projects may be a reaction to perceived need to replace other stuff that's annoyingly unstable over periods of 5-10 years, etc.
Some churn is introduced by trying to keep up with a changing language, standard lib, or other dependencies, but some is just adding features forever or endlessly refactoring aesthetics under different management. Makes me wish for a project badge to indicate a commitment like finished-except-for-bugfixes.