[wpietri]

That's a plausible direction, but what I'm looking for is then a detailed analysis of what constitutes job-ness.

Another possible line of inquiry is mastery. We're a tool-using species and we definitely have some disposition to skill acquisition and skill perfection.

A third would be something related to wealth acquisition. That idle games burst through the diminishing returns curve by continually upping the game, overriding a mechanism that keeps us from over-focusing.

And I'm sure there are more possibilities. Which is why I'd love to see an analysis of the game mechanisms, as I think it would narrow the hunt.