I'll add in another voice for "off topic", but I'll give another reason: Speculation.
There are many things that could explain the "urban legends" you list. The Loch Ness Monster could be a plesiosaur, an alien, or a series of hoaxes. Area 51 could be inhabited by little green/grey men, or it could be a U.S. military base that is completely straightforward.
The test question you wrote up (though now off the table) was complete speculation. The last time I saw it before it was deleted, it had four close votes: two for off topic and two for primarily opinion-based. I was one of the latter two voters, because there are many different explanations for the disappearance of the colonists at Roanoke. Nobody knows the truth.