because there is the opposite fallacy which is also derided: the one where the best engineer in the team is promoted to be a manager and in turn no longer does much/any development work.
The bottom line is that while there are great people out there, most people are average or worse (bell curve 101, sorry) and they end up progressing up the career ladder too.
I tend to see people on three paths - they're an engineer and they want to keep coding and getting rewarded for that; or they're an engineer who wants to manage process and people; or they're an engineer who wants to focus more on architecture and design. The person you want to "manage" is the second one - they've a working knowledge of how the tech works but they're actively developing their leadership skills.
Leadership skills are no different from any other skills - they can be learned. In some cases people show more of a "natural" skill in that area but that doesn't meant that it can't still be learned - it'll take you out of your comfort zone but you don't tend to advance unless you do that.