There is a fundamental flaw with these kinds of sites. Early on, they're great. People ask questions, the questions get attention, they get answered, there is a healthy active discussion about the topic.
Then... all the common questions get asked, and so anyone asking a question that already has an answer gets their question shot down. Because, you know, you're expected to thoroughly research the site concerning your question before you're allowed to ask it. Once a person gets shot down asking questions a few times, well, they don't tend to bother any more.
Worse, this policing tends to err on flagging things as a dupe, so things are mistakenly considered to be the same question. Then, the valid answers for a question can change over time, because technology / versions of things have evolved, however, since the question isn't asked fresh, it doesn't get the attention and focus of experts to create new answers.
So over time it goes from "ask questions" to a essentially a static Wiki, but in a suboptimal question / answer form, without any good categorization of things based on versions and so on, and no good way to focus people to questions that need to be "re-answered". A question about MySQL from 10 years ago has answers, but now those answers are out of date. Sure, they have a rating system to upvote / downvote answers, but since it's just a mass-democracy type thing, answers can have a thousand up-votes (from all the attention it got early on), become out-of-date, and never get enough attention to down-vote answers that are antiquated. I have come across questions that have MANY answers, and the top 4-5 answers are no longer applicable, and find one with just a few upvotes is now the correct answer.