I answered this under the question, but to give an official answer on Meta:
See this page for information on Closed Questions. To quote the relevant section:
Questions that need
additional work or that are not a good fit for this site may be put on
hold by experienced community members. While questions are on hold,
they cannot be answered, but can be edited to make them eligible for
Questions that are edited within five days of being put on hold are
automatically added to a reopening queue for community review.
Questions that are not reopened within five days will change from [on
hold] to [closed].
In other words, if the OP disappears from the site (as many, many identify-this OPs do), their question is closed after five days. If not, they can edit it and add details. Then, experienced members of the site are notified about this (I think experienced = 500 rep and above. See here.) If these members feel enough detail has been added to the question, it is reopened.
Many of the questions put on hold are either off topic for the site or, in the case of this question which I think led to your post, are far too broad and generic. Remember, we're not just trying to get an answer for the OP, but one that would be useful to future users as well. When so little information is given, it's hard to imagine how the question is useful to people in future. Additionally, it's likely a large number of correct answers could be left, which only the OP and no one else could deem as incorrect. This is the same reason why list questions are off topic. If a more concise question were given, it could be useful to future users and would produce a much smaller amount of potentially correct answers.
I do however agree leaving comments is the best thing to do. It's helpful and particularly for new users is a nice introduction to the site.
So in summary. To answer your question:
Why are people so quick to jump on the close vote when the reason is "not enough detail"? Give them a chance to update/edit
That's exactly what voting to close a question does. It gives them a chance to update/edit it.