Not OP, but generally because they aren’t doing the work I need them to. In my experience some folks literally don’t know what they’re supposed to do to get started or get stuck on small tasks. Micromanaging is a way to get past those blocks. That said, I absolutely hate doing it and it runs counter to my entire people leadership philosophy (it’s a waste of time for me and condescending to the employee). But at some point you have to get work done, and if that takes micromanagement, so be it.