Perhaps there is a community-wide phenomenon of progression, but not observable within single projects? I wonder if this may be similar to the "won't hire jr.

Perhaps there is a community-wide phenomenon of progression, but not observable within single projects? I wonder if this may be similar to the "won't hire jr. developers" tragedy of the commons that many companies are party to: the economy as a whole would benefit from investing in jr. developers (by providing an environment in which they can advance to sr. developers), but for each company individually, there is risk in training someone up in a year or two only to have them leave and become a "mid-level developer" at another company.