Management requires a birds-eye view of the project in all its breadth, and quickly responding to issues, as well as reporting up (proactive stakeholder management). The job of the manager is to keep the CXOs happy (inform/manage expectations) whilst protecting their own team so they can focus on getting their work done with minimal disruption (isolate).

Coding requires the opposite, zooming deeply into the code and retaining focus. The job of the IC coder is to deliver (design and implement) beautiful and pragmatic architectures that do what is expected.

I recommend anyone to reject to fill roles where these two are combined into one. Note that this is not a comment about workload, but about irreconcileable differences. (The perfect candidates for each even match different personality profiles...)