I often come across questions that are simply points of curiosity rather than requests for help to overcome a development problem that is blocking progress.
Examples of these might be “Why is the number of bits in a word always a power of two?“ or "What kind of parsing engine does Perl use?".
While these examples may fall foul of the rules for other reasons, I can see nothing in the list of reasons to close a question that covers such idle curiosity.
Have I missed something, or should a new category be added?