Some technical people are terrible at helping juniors in their careers, and relatively poor communicators. Their job is "get the thing built" or "maintain the servers".
Managers support each report in succeeding not just at their job but their career, and are an escalation point for cross-team conflict, among other things.
Just because somebody's job-description says something doesn't guarantee that persons contributes anything -- e.g. the CEO of yahoo who refused to buy google for 1 billion dollars.
Leading is having an affect on those around you such that they voluntarily look to your for input.
Any role at a company can do that, so to try to pretend that falls directly on management lines is a white lie managers tell themselves.