If they know the documentation exists, then either they should RTFM or explain how they did and didn't find the answer.

Ie, "I looked in the docs and couldn't find how to..."

Yes but some people ask questions rather than try to look for answers in the documentation, since it is perceived lower effort than looking in the documentation themselves. It is quicker to ask a question than look through the documentation, especially if you are not sure about the right keyword for your query. Plus if you ask a question you get to define the criteria for a valid answer to include an example that almost exactly matches your situation.

Edit: I feel like I should point out that I agree that RTFM is an incredibly offensive term, but some form of answer like: “it is covered in the documentation” actually conveys one important bit of information: The answer can actually be found in the documentation.