mm hmm, and uh huh are also very colloquial. People say them with their friends and family all the time, but they are considered unprofessional if used in a formal setting.

It's just hellishly annoying to listen to, especially if you have to listen to the interview again. So the participants in the interview mind their speech in order not to sound unprofessional.

Most of those are just used to give the speaker time to think between words or sentences. They don't affect the meaning or tone of a sentence, and people largely regard them as a sign of uncertainty or a lack of self-confidence. They're commonly used by most people in virtually all situations just because not many people are skilled public speakers. If people really want to impress someone they may make a conscious effort not to say these "words", but a lot of the same they accidentally say them out of habit anyway. Parents constantly correct their children if they say "uh", "um", "mm" etc. No one wants to say them because everyone wants to sound confident, but without lots of practice people can't help but add these sounds when they need to pause when speaking.

May be because it kills the conversation. Since it's closed end type reply. You can't ask more from interviewee if you're interviewer & give more details if you're interviewee. There is more chance of information extraction if you say,"but i don't agree...", "are you sure?", "i doubt..." etc.