Interviews (by design!) simulate intense interaction between the interviewer and the interviewee, similar to a workplace situation when trying to solve a problem. That setup is not objective.

The result, even just the code itself, is also not judged on a binary yes/no scale, which again leaves a lot of room for opinions and bias to muddy the water.

I've done hundreds of engineering interviews. Conducting objective interviews is very hard. Anybody thinking they are objective either has never done interviews or is fooling themselves.