Because interrogations are intended to coerce confessions, interrogators feel themselves justified in using their coercive means. Consistency regarding the technique is not important; inducing anxiety and fear is the point.
“Never let a problem to be solved become more important than a person to be loved.”
“And trust, yes, which is important, but that is what I aim towards. Now that is difficult for some people, and with that desire to get things as good as possible, I would say that I'm probably regarded as quite prickly to work with.”