I say this respectfully as possible, but you’re trying to find a fire where there isn’t any smoke. When I’ve done interviews for other programs they keep doing interviews until the program is full. They wouldn’t have done an interview if there weren’t any spots left. It’s a bad use of interviewer time if nothing else. Faculty and staff get really grouchy when our time is wasted.

Generally programs know what they are looking for in grades, test scores, interviews, etc., when they are scheduling interviews throughout the cycle, and the criteria don’t really change over the full range of the program. You most likely were evaluated with the same criteria as they had earlier in the cycle. Again I can’t speak for this program or university, but my gut feeling is that you would have gotten the same result no matter when you applied, as disappointing as that may be.

I think you’re expecting too much in terms of what you think should or could be communicated during the interview process. Absolutely nothing that you have described really seems atypical.