There are numerous reasons why developers are difficult to manage. One of the main reasons is because by and large they are introverts. They therefore don't communicate well with other people at all times.
Also - let's face it - the work developers do isn't always easy to understand and quantify; as opposed to say building a house where the inputs/outputs are clearly visible. I can't imagine being a non-techie and trying to manage a team of developers would be at all fun.
Source: I own and run a software development company and have employed and contracted with dozens of developers.
Social HR huh? Yeah.