I would like to know why questions can be closed in general; it just occurred to me that even if the question does not make sense to you, there is no reason to close it and prevent it from ever being answered by someone else. What is the point of closing questions?
It seems that the underlying assumption of the original question here is that questions on the main site are closed because they "don't make sense" to the close voters. This is an erroneous assumption.
The principle goal of the SE network is to create repositories of discoverable, searchable questions with high quality answers. The idea is that a user's typical interaction with the site will occur when they search for a question (using the on-site search, or a third-party search engine) and find that it has already been answered. The goal is for 90%+ of users to never have to ask a question, because their answer is already on the site.
(Note that this is distinct from other services, such as Quora, which seek to answer individual questions as they arise.)
Because the principle goal of the site is to create a searchable database, it is necessary to ensure the quality of that database—we don't want the noise to drown out the signal. As such, it is necessary to close (and delete) questions which are not a good fit for the site. There are a number of reasons why a question might be a poor fit:
- the question may be too local (i.e. interesting only to the person asking the question—things like homework problems often fall into this category);
- the question may provide too little detail for a future reader to find it via search;
- the question might be a duplicate of something already asked;
- the question may not provide enough context for answerers to understand what kind of answer is actually expected;
- the question may be simply off-topic (i.e. not actually a question about mathematics);
- and so on.
Hence questions are often closed for any one of myriad reasons. This is part of the basic functionality of the site.
I'll give a simpler answer, it's because people don't usually specifically 'search' for questions when trying to answer them, it rather pops up in their feed. If a person who has intent to answer sees many questions poorly presented / frame/repeats, their morality of wanting to answer will decrease.
If there was somehow a neuralink system which would automatically look at the things in our brain and find the answers for questioners (supposing some questioner would be interested in the non standard questions), then sure, I would agree with what you are saying.