Senior Developers are often running the interviews. If the Senior decides you need to know a certain set of questions for the job, and you fail those questions, then they feel you aren't ready for the job. That's not to say these questions aren't often ridiculous, but we're also forgetting that many Seniors (such as myself) don't ask these questions, asking simpler, more practical questions, and probing for industry knowledge. It's my own finding that around 50% or more of candidates can't write a single line of code at all. So asking a question like "reduce this array" is sufficient enough to judge that person's ability for the job that I need most of the time.