There's very little room for deviation as well because it is so formulaic. Present a novel and interesting system? It may not be realistically solvable in a 3

There's very little room for deviation as well because it is so formulaic. Present a novel and interesting system? It may not be realistically solvable in a 30-60 minute session to a satisfying degree because the candidate doesn't have familiarity. From the candidate side, you can take a risk and make it more interesting by presenting more novel solutions, but the interviewer might be looking for very specific response patterns; "signaling" of a sort. So both sides just stick to a narrow range of scenarios and responses. Once you've done one or two, it's hard to see how you couldn't do every other one after it.