I am sure that if someone is uploading the specific wording of an interview question, then that would potentially be a copyright violation. But if they're just describing the problem in their own words (for instance "I was asked to design a system for selling movie tickets") then there shouldn't be a copyright issue.
Not sure what the legal technicalities are, but one of the questions I saw on the site was just a picture of a the user's screen with the question on it, so it's definitely more the former than the latter.
Yes, the bar for copyright protection on written text is very low. And I've never not seen them just plainly copy/pasted.
If someone rephrased them I really wouldn't have an issue with that, because the phrasing is fairly important to the particular questions I'm asking. (and the doofuses using these sites probably would miss any nuance when rephrasing them anyway)
I am sure that if someone is uploading the specific wording of an interview question, then that would potentially be a copyright violation. But if they're just describing the problem in their own words (for instance "I was asked to design a system for selling movie tickets") then there shouldn't be a copyright issue.