Well the idea is that they aren't memorized by chance first, they are known pretty well because ideally you have a track record of applying them to real life problems (even if they are just school projects or side projects). I can describe times I've used queues to solve various problems, for instance. The other thing is, as others have pointed out, seeing how someone breaks down and approaches and unfamiliar problem is very valuable.

It sucks that we have to do it under the pressure of a 45min-1hour conversation, and I totally get that the stakes are high and so nerves are a problem. In general I think the best way to handle this stuff is to give candidates multiple paths to succeed.

I think the nerves problem is slightly overstated though, because I do think many companies do give candidates multiple paths to succeed. For instance, if you have trouble performing well in an interview setting it's pretty crucial that you have a wide array of work on github proving you can code and that will give you an opportunity to have some complicated but familiar code that you can talk about in the interview. If someone comes in with this but is shy or gets frustrated or something, as an interviewer I'm really going to try and pull the magic I see in their github out of them in that interview. Keep in mind that people hiring engineers really want the candidate to succeed in most cases. It's so difficult to find good talent that while I'm never going to lower my standards to hurt the company, I'm definitely on the candidate's team in an interview, trying to get them to shine as best I can.