To ensure filling PGY1 positions and avoiding the SOAP, it's only to a program's advantage to rank as many applicants as they can unless they find some candidates simply unacceptable. Programs often have an idea from prior years of how far down their match lists they've gone to fill their positions. With that info in mind, programs will simply rank as many candidates they can be confident filling with. I know of some programs that end up striking 15% of their interviewees off the rank list, but that percentage will obviously vary among residencies.