I think it's a mistake to think of whiteboard problems as attempting to recreate a real work environment. They are a proxy for the kind of quality you are looking for that can be "measured" within the alotted time.

They can show that the person is prepared (they studied), generally knowledgable (they remember obscure stuff), or just clever (they come up with interesting approaches to the problem).

I'm not surprised you see both excessively simple (make sure they aren't ridiculously unqualified) and excessively obscure problems, since the first one essentially tests your reflexes and the second one tries to determine if you learned your job "by rote"

They’re used because “that’s what company X uses”. People are cargo culting each other, and making up post hoc rationalizations for their behavior.

Unless you work for a major tech company where optimizing the false positive rate is your primary concern, using these problems is counterproductive.

Yeah, it's philosophically valid that you'd want to measure certain critical things that are different from the everyday grind.

But I think the simpler explanation is that these interviewers mostly had picked "cool" recursion problems.

I did get the job, and seeing $BigCompany's hiring process from the inside didn't contradict this.

You can solve most recursive problems with a loop and a stack. That way you aren't making a bunch of function calls eating up memory.