It ain't random....
All the DCO IWC kits go to the same board.
They then get screened for completeness (i.e. qualified to apply for an IWC designator, not missing any documents).
Assuming your kit is technically correct (qualified to apply, no missing docs), it gets racked/stacked against other kits that have the same designators listed #1 on the application. If there's a toss-up, where a candidate would fit more than one designator, then the board may try and optimize/maximize quotas by selecting someone for their #2 (or even #3) choice.
I've seen the list the past couple cycles (this most recent one excepted). It lists which kits are DOA and the reason(s) why. Sometimes is the applicant's fault. Other times, their recruiter didn't fully understand the requirements and forgot to request specific information from the applicant.
The DCO IWC program is way oversubscribed (really just 1835/INTEL). Even with 50+ quotas per cycle, someone just ain't gonna get picked. Keep in mind, these are folks who are academically/professionally qualified and likely some of the best applicant's their respective recruiters have see in a given cycle. It sucks to be told, "You're great, but I'm out of slots, try again..."