Sure, but this isn't about investigating individual jams (and what could be done even if so, anyway, if they "have the right to decide who can and can not participate"? I mean, participants can't even ask for a rationale?)
It's about how there's no field at all... no possibility for them to even leave an explanation (unless I missed something it's the same interface that submitters get when they remove their own submissions too... and no rationales for submitters would make sense, but not for third parties). Literally, the only way they can say anything is to do it in the comments before removing it, and leave some time for the submitter to see it (or... leave it on the game's page, since PMs don't even exist here)... which obviously not all people would be patient enough to do. This actually happened in multiple jams that I noticed... and noticed is a key word, since it's all so subtle. Just horrid UI design... rationales should at least have fields to be put in, otherwise obviously they're not going to leave any...
Surely, if *any* type of 'question' by the hosts can be 'required' (and I've seen some utterly dumb, non-require-worthy ones), then rationales and their fields should be required too! Otherwise, really, why would anyone be motivated to spend hours on something that can be removed without even a single word as a rationale if hosts were so inclined? (Besides inclination, of course, the worst is that the site incentivizes them...)