It is hard to fit all the common off-topic close reasons we use into 3 large categories. If our goal is to give the best feedback to the authors when putting their questions on hold, why are we restricting the number of custom close reasons to just 3? Shouldn't we have a bit larger number of custom close reasons (e.g. 7) if they are commonly used?
One more thing, I noticed that the size of custom close reasons is 400 characters while the size of comments is 600. It would be nice if the size of custom close reasons is increased to 600 characters so we can keep using what we were posting as comments when closing questions as off-topic in the custom close reason's box.