Because liking someone doesn’t mean they can do the job. Just because you’re excited about a problem domain and someone else seems to also be excited doesn’t mean the can or will do the job well. They probe for past examples of you doing a job well because it’s a proxy for you doing a future job well. They acknowledge any interview process is imperfect but they also decided randomly pointing at resumes and saying “tell me about X” either doesn’t correlate or correlates negatively. This is in addition to the bias problem which was the other big reason they gave.