What are the reasons why closed questions cannot be answered? (Particularly: closed as not a real question.)
That's the purpose of closing a question - closed to answers.
A closed question indicates that a part of the community doesn't think it belongs on the site (for whatever reason) and should probably be removed later on completely.
Giving answers to closed questions would mean that askers would have no incentive to keeping on topic and post high quality content.
As for "Not a Real Question" - if it isn't a question, it can't have an answer, can it?
Because a question which is not a real question
...cannot reasonably be answered in its current form.
and therefore the answer probably wouldn't be very useful. We close a question to signify that it isn't a good fit for StackOverflow. Allowing users to answer bad questions would mean two things in particular:
- Users would have no penalty for posting bad questions, and therefore would have no pressure to post good questions
- Answers would almost always be totally meaningless, or too broad