Follow up questions will vary, but the bulk of most interviews is the same for every candidate, and candidates are then judged based on a rubric that is the same for every candidate (though often tailored to the specific role).

The consistency lets interviewers compare across candidates, and avoids the cognitive pitfall of defining a rubric after-the-fact that lets us hire the candidate who appealed to our lizard brains.

Even at startups, questions are also usually tested on several existing employees before it is used on the first external candidate, for calibration. Companies put a lot of time and money trying to hire for actual competence.

Yes. It was a programming exercise that took me a few hours to create. It was not practical to re-make it for every candidate.

BTW, it's industry normal for companies to come up with a programming exercise and reuse it.