Why are there 3 votes to close the following question?
It seems like a perfectly legitimate (and interesting) question to me.
The currently chosen close reason are all the "Lack of context" reason (you know, with 17.1k you can click the close button and see the currently selected reasons without actually committing to voting to close).
This suggests that the voters who have voted to close have done so because the question is given in the form of a "Problem Statement Question", and would prefer the user to include
For further reading: see https://math.meta.stackexchange.com/search?q=problem+statement+question
That said, in the specific case you linked to I am inclined to agree with you that the question is perfectly legitimate. Though having some more context etc. cannot hurt.