Part of the problem is that the discipline is very wide, and there's different mixes of skills needed:

    +-----------+
    |\ business | - excel macros
    | \     +   |
    |  \  users | - web dev
    |   \       |
    |    \      | - back end dev
    |     \     |
    |      \    | - framework dev
    |       \   |
    |        \  | - tooling
    |         \ |
    | coding   \| - OS / compiler / database dev
    +-----------+

There's no simple cutoff that can mark someone out simply as a developer. And the diagram above doesn't reflect the fact that within each slice of the coding wedge, there's a different mix of technologies, different rates of technology turnover, requiring a different mix of e.g. aptitude to pick up new technologies quickly, vs depth of experience in existing technologies, quite apart from what the specific technologies are.