I think you're confused about the phrasing of the title. 'Why/ why not X' can be a request for information as you seem to imagine, but it can also be a proposal, as in 'why don't we have both'?
Sure, but that's belied by the body:
> Does anyone have any insider information or generally good theory as to why YC's own job posts include none of that information?
I think you're overthinking this. It's chat, not code.