But first, why is this even important? Do managers have a place? Aren't they mostly the problem in many organisations? Haven't we all left jobs because of our awful managers? 

Just because you are good at your job, whatever it may be, it does not follow that you will be a good manager in that context. The skills of management and leadership are well defined and they don't grow on trees or come upon you by osmosis. Many of the people I work with have suffered from what's been called 'the accidental manager' who knows all about the job but not how to facilitate and lead others to do their best work.