Don't over analyse what a "quality post" is. It's simply just a topic/reply that's decently original and does actually help people in one way or another, or at least contribute to the topic. That's pretty much it. No guidelines or anything. Skills though? Well, bitcointalk is a bitcoin forum, so of course you need to have decent knowledge in bitcoin or cryptocurrencies in general; which is something that most people here are mostly missing.
Like sometimes I saw some posts maybe sharing some information of a particular topics but they are not being awarded.
Yes, indeed there are some topics/replies that didn't receive any merit. But people are overexaggerating the number of topics/replies that aren't given merit. I guarantee you that if a topic/reply is good, there's like a 95% chance that it has at least one merit or if not, then chances are that not enough people has read the topic/reply.