Why do hiring managers invite unqualified candidates to interviews?

I have been to several interviews lately, and I have noticed that many of the interviewers are usually not very impressed with my credentials. I have wanted to ask them more than once why I was invited to the interview in the first place, but preferred not to because I don't want them to say *that* was the reason I did not get the job.





Any ideas as to why they do this? I imagine they try to make the point that I am unqualified for the job in order to rationalize the fact that they just did not like my accent, or my clothes, or my haircut, or my attitude. Otherwise why waste their time interviewing unqualified applicants? I am not a psychologist, so that's just a thought.
Why do hiring managers invite unqualified candidates to interviews?
I think they do to make sure they have a quota of races apply for the job.
Reply:They are racking up "interest" in the job.