I have had a look at this question, which just seemed rather longwinded to me. I also learn that it once had a different form. There is an art to getting the right answers at the right level on SE (and generally I suppose). I am not sure what form of the question was answered by who.
One issue with several physics topics (like foundational QM) is that there are different mathematical formulations of the same material, as well as different interpretations of some of it. What happened in this particular case is that the original question asked about the formulation in a standard textbook. Clearly that question can be answered. So also could be answered about other formulations which have certain advantages, or which some researchers like. Of course different mathematical formulations have to be shown to be equivalent, so assuming that, other formulations are relevant to the question in a sense. However you were not interested in non-standard (or at least non-textbook) answers to the question.
Also in this case the person answering had only just learned of these techniques themselves and so could only provide references rather than explain anything line by line.
So that is what happened.
A broader issue (which was in another remark) was about the legitimacy of providing "answers" not appropriate for the OP, but which are appropriate in some broader SE sense. The quote was
In general, even if it were suitable only for Albert Einstein it has to be posted here
I quite like the quote, but I dont know what the SE policy is on this one. One can see both sides of the argument on this.
This was stated because of the concern that any duplicate would be closed. Consequently even Albert Einstein would get his duplicate question closed in favour of yours, and so he would want to see all the other mathematical arguments presented as Answers to your question. On the other hand maybe Albert Einstein would also need to learn how to ask his duplicate question in a way that it doesnt get closed, by refering to your question and then saying "I would like to see much more mathematics and philosophy than discussed in these answers." Maybe that wouldnt get closed, but you see the dilemma.