The question is whether that would raise more objections and protests than it would answer. Almost everything we do is defensible to the community, because if it weren't, we wouldn't do it in the first place. I say 'almost' because we make wrong guesses, but then we're happy to admit mistakes and fix them. That doesn't mean it's all self-explanatory, though. On the contrary, it can take a long time to explain because there are many complexities, tradeoffs, and non-obvious aspects.
Meta threads and discussions tend to invite objections from the litigious type of user. Such users are rarely satisfied, but have a ton of energy for meta argument, so it's easy to get into a situation where any answer you give leads to two or three fresh objections. Such objections have to be answered with great care, because if you slip up and say the wrong thing, people will use it to drum up a scandal (edit: and will quote it against you for years to come!). This consumes a lot of mental and emotional energy. (Edit: btw, this is asymmetrical: the people raising objections and making accusations are under no such restriction. They can say anything without downside, no matter how false it is or what they accuse you of. They can make things up with impunity and people will believe them by default, because on the internet you are guilty until proven innocent, plus everyone loves the underdog. These are additional reasons why it's easy to end up in a situation where every comment you spend an hour painstakingly composing earns you a bunch more counterarguments and demands.) These arguments tend to be repetitive, so you find yourself having to say the same things and defend against the same attacks and false accusations over and over. This is discouraging, and there's a high risk of burnout. Disgruntled users are a tiny minority, but there are more than enough of them to overwhelm our limited resources—it ends up being something like a DoS attack.
I fear this outcome, so we've always shied away from adding such a system. We want to be transparent, and we answer whatever questions people ask, but it feels safer to do it ad hoc as questions come up. There's no specific question you can't get an answer to, other than a few special cases like how HN's anti-abuse software works.
There's an opportunity cost issue too. The vast majority of the community is pretty happy with how we do things—I know that because if they weren't, we'd never hear the end of it, and then we'd say sorry and readjust until they were. I think it makes more sense to do things to keep the bulk of the community happy, or make them happier, than to pour potentially all our resources into placating a small minority—especially since, once you've done this job for a while (say, a week) you know that nothing you do will ever be completely right or please everyone.
On the other hand, if I could ever be persuaded that a full moderation log would satisfy everyone's curiosity and reduce the overhead of misinterpretation, complaints, imagined malfeasance, etc., then we'd be happy to do it.
This question has come up repeatedly, so if you're curious to read previous answers, see https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que....