Your flag detail stated
This should really be converted to an answer as it solved the asker's problem.
There was a couple of reasons here.
The first is that Moderators cannot convert comments to answers. Frankly I don't see a reason for us to need that power either, we can't force people to post an answer and we shouldn't even if we could.
Secondly you, or indeed anyone, could have posted an answer stating "OP confirmed that Sticky keys was the problem" without needing moderator intervention.
Thirdly, the comment on its own was useful. Lacking any ability as per my first point, or activity per my second, there was no reason to delete it.
There was nothing for a mod to do so nothing was done and your flag was declined as a result.