What are the other reasons? Maybe you could enlighten the rest of us, because I've never been able to figure it out.
Not sure if this is a serious question or rhetorical, but I'll assume the former in my reply (yes, I know this is slashdot).
First, it's not uncommon for an employee who has little or no managerial experience to "not get" what managers do so in my jobs where I've had a significant managerial role (e.g. dept head or VP), I try to make some specific information available for staff. For example, if you reported into me at any level and you came to me with this this question, I would pull out your job description and the one for your manager (assuming you had the same job family) and I would review them side by side with you and answer any questions you had.
But speaking generally (I've had everything from IT to Medical Affairs report into me at various times), some of the things I expect from first line managers (different from their direct reports) are as follows:
- Managers are expected to perform at a "role model" level in their specific technical area. As such, they can perform QC/QA activities as needed (especially for junior or recently promoted staff) and are themselves accountable for technical screw ups.
- Managers are expected to model business competencies for their group. For example, I expect them to be able to communicate well with customers and colleagues, which I don't necessarily expect from an individual contributor, depending on role.
- Managers are personally financially accountable for the success of projects their staff support, and they are "graded" not just on their personal contributions but those of their staff (usually I weight this more to group contribution as a team grows). As such, I instruct new managers that they are not expected to do the job of (e.g.) three people, but to make sure that three people can get their jobs done. This does not mean that they get to use a stick often to whip their employees into longer hours or crazy commitments, because that sort of management is counter productive long-term, but it does mean that managers have to identify and solve problems that limit productivity. I.e., they must continually think "one step ahead"
- Managers are responsible for hiring, training, remediating, and terminating their employees. All of these are time consuming when approached correctly. If you've never been involved in remediation efforts, then I will simply note that that they can take anywhere from 3 months to a year to go through a full process of performance evaluation and documentation, depending on the procedural rules of your organization. Termination for performance is and should be relatively rare, and a manager that decides to go this route better know that their own competency as a manager is called into question. What I've unfortunately had to call upon my own line managers for this year is down-sizing support. And it's really easy to be cavalier about this sort of activity if you haven't been through it before, but it can be a soul sucking experience to have to dismiss your employees for whatever reason. (I don't have or keep managers who don't care about their staff.)
- Managers support the company. I'm not saying that you can't like your employees or fight for them (you better if for no other reason than it's your job to retain them), but when something like a strategic business decision is made, you either get behind it or you find a new job.
Granted, there are radically different philosophies about management so ask someone else and you may get a very different answer. That said, I don't think there is anything in my response above that is novel or uncommon.