The problem is that metric, like any metric, is both easy to game _and_ can provide misleading information.
Measuring number of commits? Create fewer, larger commits. Measuring commit size? Pull in more third-party libraries, even where it does't make sense. Author count? Add more/less documentation and recruit or inhibit new devs depending on what your goal is.
Not to mention the number of commits/authors before and after an arbitrary point in time might conflate a successful growing project with a project in a death spiral being passed around from group to group.
It's a good idea, but in practice simple metrics like this often (but not always) devolve into prime examples of Goodhart's law.
Measuring number of commits? Create fewer, larger commits. Measuring commit size? Pull in more third-party libraries, even where it does't make sense. Author count? Add more/less documentation and recruit or inhibit new devs depending on what your goal is.
Not to mention the number of commits/authors before and after an arbitrary point in time might conflate a successful growing project with a project in a death spiral being passed around from group to group.
It's a good idea, but in practice simple metrics like this often (but not always) devolve into prime examples of Goodhart's law.