I have no statistics available, but when you take a "tour" in homework tagged posts, the ones that are on hold, usually get closed; not due to moderation strictness, but mainly due to the asker's neglection.
Imagine that you have a question about chemistry assignment your teacher gave you. You come over and ask it in the SE, then 2 hours later you see it is put as on hold by moderators. They ask you to put your own effort in answering, whether it leads to a final and correct answer or not. It's possible you were only looking for the answer and in other words, making SE write your homework.
Or maybe, as I believe some users' intention is that, you were facing a problem in chemistry you have never seen before, and are asking to know "what main concepts does that question relate to?" Or maybe, you have been dealing with this type of problem for the 1st time and want to know the scientific approach a chemist will make to solve it. (the two groups are different: While the first doesn't know the laws and formulas for the solution, the 2nd group only has problem using those laws.)
The latter two types of askers, when asked for a solution, will get baffled, and therefore, won't intend to do any corrections to their post. How should we assist them? Of course we shouldn't give them the bare answer, but shouldn't we keep them from leaving and not watching their back? (I used lots of shoulds:))