>>Being able to talk and interact with people is a part of the role. Software is not written in isolation - it is done best with a lot of collaboration and critical review of work. Being able to communicate and give and receive critical feedback are cornerstone traits. Good code is not written in isolation and giving and receiving critical feedback is not comfortable.

There is a difference between collaborating and receiving critical feedback from a fellow coworker, and being evaluated by an interviewer (or worse yet, a group of interviewers) who might or might not offer you a job (since your livelihood depends on that). That's why people who are typically comfortable working with others can become extremely anxious during whiteboard interviews.