Some people don't have their own drive and rely entirely on expectations set by leaders. Specifically, they will say they're working on something and might even get it done but they could have gotten it done faster and possibly better with at worst micromanagement and at best genuine coaching.
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.
Not the OP, but the one time I had to micromanage someone was because the engineer was unable to focus on the important tasks and would deliver nice things but totally unrelated to the end goal...