An interesting and demanding topic..
I too have the impression that it is not a very big thing in real life more a sort of myth -?
Murder is one thing, as in non-consensual killing, but I do assume that it is the other thing we are talking about here?
This I see is the core of the matter. I see the view here (with you and other people) that if you consent to your own death you are out of your mind and should not be allowed.Of course one reason you may not have heard about it is the fact that it is horribly and totally illegal. IMO it also breaks all three elements of safe, sane and consensual (even if the person consents to being killed I am not sure should be possible to consent to your own death, it certainly isn't legally and morally it is a nasty area of personal freedom to explore).
I have another view: Any person owns themselves. If you cannot own yourself, then there is not real freedom and that, to me, is the single most important thing in life.
The consequence of that is that you also can - for whatever reason - decide what to do with yourself, including dying as in suicide or agreeing to or asking someone to kill you.
Why anyone would want to is beyond me, but that is another matter. I see it only from the point of view of the person who decides on death him/herself.