Because they're stupid?
I'm with you, I can't think of a single good reason to not rank a program you interviewed with. Not one. No sane person would rather go through the scramble.
You clearly have not been out on the interview trail.
I agree that some programs may be perceived to be horrible, but what seems strange to me is that people only realize this after an interview day without realizing it when they applied. I dunno, I guess it's hard for me to imagine how an interview day could be THAT bad.
Again, wait until you hit the interview trail.
ALL programs look fantastic
on paper. It's very much like internet dating. Some guys look great on their profile....and then you meet them in person, and they're feeling up waitresses, being rude to bartenders, and smashing their fists into walls if someone cuts into line in front of them. Not good.
There are some genuinely awful programs out there that, by normal standards, look fine. I remember interviewing at one program like that last year. On paper, it's a great program. They train their residents well, their grads get into fantastic fellowships, etc.
During the interview day, though, 3 of the interns looked exhausted, beat down, and on the verge of tears. The faculty had their faces twisted into a rictus of fake good cheer, and left as soon as they could. I overheard 3 senior residents talking about how much they hated the junior residents. One junior resident said, "This program...isn't....THAT...malignant." Etc.
I had classmates who went to interviews where the program director would say "We're in compliance with the 80 hour work week," and the residents in the back would snicker derisively. Others went to interviews where interns would pull them aside and say, "If I had to do it again, I would NEVER come here. EVER."
Yeah, some places really are THAT bad.
Makes perfect sense to me. What makes it even more stupid is that should you omit certain programs and somehow not match, you can't even really scramble for open spots at the schools you rejected.
Of course you can scramble for those open spots. If you're in the scramble, all open spots are fair game for you. Why can't you?