In general, "Why is question X treated different from question Y?" isn't a real good question. Well, they're nearly three years apart, different people participated in each, maybe a mod hadn't drunk coffee that day, etc. Proof by "but but another question"question did it" is never helpful. In fact, if you see something wrong with an older question please feel free to flag it or perform other corrective activity, as mods don't read every post on the site.
In this specific case, the questions are not duplicates. The earlier one is about "I have players that don't bother to fear death, because I don't kill them ever." This question is about "A guy has a stack of character sheets and doesn't mind dying." Not only are they very different, they thus demand a different level of Back It Up!. Most every GM has had to struggle with the balance between killing PCs and not killing PCs and its effects on PCs' attitudes toward the world - I think it's fair to say that's a basic GM technique. Thus there's a lot less demand for Back It Up! on the first question (and some of the answers do cite experience). This second question, someone with a stack of characterscharacter sheets, is obviously much more unusual and we'd like to hear from someone who's dealt with a serial character-suicider to understand how to handle that.
Even the previous question you link didn't go down super smoothly, as you can see from the comments and edits and such on it, and I can see from the flags, deleted comments, and load of short/partial answers (these even generated an automatic flag from the system to us - "hey there's a bunch of kinda junky looking answers appearing on a question, want to go check it out?")
The question hasn't been deleted, it's just put on hold for improvements to be made, which is not some crisis. I find most of the angst around stuff like this is driven by people taking "on hold" as other than what it's meant to be, a temporary hold to improve before we get even more junky answers.
Good Subjective, Bad Subjective and Back It Up! are crucial to running a site like this. Gamers have loads of opinions, and they all think they're smart enough to answer someone else's question even if they have never done that thing. If this were my question, I would very much want to know that an answer was "I had this problem, here's what I did and here's what happened," not "oh a random guy brainstormed me something that might work or might backfire or whatnot because they have absolutely zero experience in what they're talking about." I am not going to argue here for why we use GS/BS and Back It Up! - we do, and we're not going to stop.
The community, like any other, goes in waves. We've had times where everyone generally understands GS/BS, writes good gm-techniques type questions and answers show experience. Then we have times like now, where we have new users that haven't run across it yet from the sea of rules-questions, and an answer gets asked and we get a dozen answers, nearly all of which appear to be pure brainstorming speculation, which is off topic here per #5 above. So more enforcement is needed in the short term to train everyone. We encourage the rest of the community to participate to make that a quicker and easier transitional period.
You like questions like this. Well, me too! Believe me, I don't stay on this SE for the min-maxing and rules lawyering. GM techniques is just about all I need/care about after 30 years of gaming. And since I'm interested in those questions, I want to hear people's real experience with that problem, not some half assed guess they just came up with in their basement. I can guess myself.
But you want freer discourse and brainstorming and no need to show experience on answers. Super, there's plenty of forums out there that do that. In fact, all of them. We can't have it both ways. The reason SE has such high quality Q&A is that we curate - we curate questions and answers, we close, we edit, we delete, we flag, and not just the mods, the community. It's why when you Google a question and get a link to a forum or Reddit or Yahoo Answers you're 90% likely to get total garbage and when you get a link to a SE you're 90% likely to get a high quality, community vetted answer. You don't have to pick one or the other! Spend some time crafting homebrew and "what if"fing on forums. Spend time asking specific questions and taking a little quality time to share your hard won experience in decent quality form here.
So the question becomes, what do we do in these cases?
We can:
Ignore it, or at best pop in some comments about GS/BS. That results in questions that get out of control, like this one, turning into junk. As I read all those answers I see lots of untested opinion that it's a waste of time reading. Or add those post notices, which are a lot of work and just perplex people it appears. Doesn't work well.
Delete answers that don't show experience and say they can be undeleted once they've been deleted to Back It Up! No one likes getting their content deleted, and it's definitely not something we intend to do regularly just because it's a lot of work on the mods. We will do this once in a long while as a "shock treatment" to get all the noobs aligned but it's not acceptable general practice.
Close the question and say "it'll get reopened if this shapes up." Now, one can say it's not the question's fault... But usually in these cases the question could do a lot better about requesting GS/BS itself, where it goes into opinionland like this is when it's perhaps not as focused as it could be. However, it's unlikely everyone will shape it up. This is the least problematic of the three solutions so far, but it leaves a good question unanswered.
Community members remember that GS/BS is what separates us from the animals. Downvote any answer that does not show experience with the situation in question, add comments explaining it should be added. This is turning into a "mod thing" because other folks aren't holding up their end. If all those answers were at -5, their owners would be falling over themselves to correct or delete them. This solution works and makes the site better.
I am in favor of #4, but it is not under my control. When #4 fails, we do 1, 2, or 3 based on our judgement and amount of energy at the time.