I am puzzled by many questions being increasingly frequently closed as "off-topic", for reasons that are not immediately apparent.
Below are a couple of random examples from the past day alone. Neither is a PSQ per se, both come from posters with at least some history on MSE (i.e. not the 1-rep users who create a new account for every homework question), and both have some indication of "own thoughts".
(Disclaimer: I have an answer posted to one of those questions, but that's not the point.)
Integer solutions to $x^3=y^3+2y+1$?: OP's "own thought" as posted was:
I tried to factorize $x^3-y^3$ as $$(x-y)(x^2 + xy + y^2)=2y+1,$$ but I know this is completely helpless. Please help me in solving this problem.
Quite obviously, the above doesn't lead anywhere useful, as the OP themselves "know", and that's the reason why they are asking here. By closing the question as "off-topic" MSE appears to say that "your failed attempt wasn't close enough for us to even bother". That's not nice.
Quartic equation and Vieta's formulas: OP's "own thought" as posted was:
I evaluate these roots, but the formulas are too complicated and I wonder if there is a different solution. If we calculate the product, the solution is complicated too.
Neither approach is a priori unreasonable, and both could be technically worked out (with enough calculation pains). But the question was about "a different solution", which is an entirely on-topic question for MSE. However, it got dismissed. Again, not nice.
For context, one other user got suspicious because the question referenced $2018$, and asked about the source of the problem, which the OP did not answer timely. Then the question was flagged for review, which it passed with 3-out-of-3 "leave open" votes. Then the same user posted "Argh!!! question and answer on this post frustrate me" on CRUDE, and within 12 hours the question received the required close votes and was put on hold.
Back to the point, the MSE manifesto says that "MSE is a q&a site for people studying math at any level", and the recently discussed SO code of conduct says "offer support if you see someone struggling or otherwise in need of help". Summarily closing legitimate questions with no good reason meets neither.
[ EDIT ] As pointed out by
@JyrkiLahtonen(thank you for the answer, and sorry for my unintentional miscue)... Just like you, I missed the point that the first question was (also) marked as
contest-math, which made my post sound to be about contest math, which was not my intention in the least. This should address your 1, 2, 5 and, to make this point very clear, I am all against cheating under any guises, yet closing a question just because it happens to involve the number $2018$ is a big unwarranted stretch IMHO.
The concern I meant to raise was about users who had honest questions, posted in compliance with the official MSE rules, but who found themselves dismissed with a summary "off-topic" closure for reasons that are not spelled out in the terse closure text, and virtually never justified by the closers in comments. That's essentially telling someone who came for math help to MSE that their question is "off-topic" here, without offering any good reason, explanation or actionable recourse. I don't think that's "nice", whether CoC or not, and regardless of whether you count yourself as a "librarian" or a "teacher".