I'm really curious about something. Most contractor jobs seem to be meaningfully distinct from the work that direct employees are performing, whether it's stuf

I'm really curious about something. Most contractor jobs seem to be meaningfully distinct from the work that direct employees are performing, whether it's stuff like security and cafeteria, or stuff that is too specialized, like short-term needs (this is the Bain thing). But how does it come about that companies have both direct employees and contractors carrying out identical tasks in their core business? In the valley, this question amounts to: how does it come about that companies have both direct employed and contractor devs? What is it about the developers that causes them to land on one track rather than another; what is it about the products that companies are building that causes them to decide to staff one with direct employees and another with contractors? Does anyone have some insight into this? This is the part of the contractors in the valley story that strikes me as really weird---the market rate for a package of skills in a firm ought to be more consistent than it it seems to be given the contractor/direct thing.