Maybe Kurt didn't want to have his dead face all over the news and decided to destroy that iconic feature of his, which maybe he felt was stolen from him as it became the poster face for a whole generation and more. And indeed, I am not aware of any post mortem photograph of Kurt Cobain. [The only photo I know of is the one where you can see his dead foot, but that hardly counts. Also, Cobain's face was entirely destroyed due to the gunshot.]
Either way, we will assume here that Kurt killed himself, even though there still are things I'd like to know about in that case. Why did Kurt wish to die? This question I will try to answer, though it is not something I think can be easily explained, even for well-known cases.
Moreover, I am definitely not going to say that Kurt was depressed and sad and a sensitive person and all. He was definitely a sensitive person, and had considered suicide before (in Rome, but also in his childhood, if his Journals are to be trusted). One thing I never read anywhere else but in his Journals was his stomach condition.
Cobain was against heavy drugs and specifically condemns heroin in the afore-mentioned Journals of his. That much is true; but it is also true that he did use heroin, and when he wrote that, he had tried heroin already. So why did he keep using heroin? The stomach condition. Apparently, he suffered extremely horribly from that stomach pain, and no doctor ever found a reason or a treatment for that. They all gave up on his case, and short of any other resort, Cobain used heroin because it was the only thing that eased his awful pain. Those of ill will may consider this an excuse, but I don't think Kurt would have needed an excuse to do heroin if he had wanted to do heroin. I don't recall verbatim how he describes his stomach pain, but I think he compares it to having a Hell inside, or that it burns; at any rate, it was a pain of the incapacitating kind, and obviously intolerable.
Of all the theories, no one mentioned this stomach pain as the possible reason – or rather, one of the reasons – for Cobain's untimely death. Do you kill yourself because of a tummy ache? I can hear you, people. My answer to this is definitely yes. I've had some overwhelming inner pains and however short they were, the idea of dying to avoid such atrocious feelings was already there, not as a plan, but as a sure exit. I also know of someone who was afflicted with terrible stomach aches that no doctor could explain and solve. This kept the person awake at night, continuously suffering, never having a break from it, for years. This person seriously considered suicide. The person was a child when this happened, and so he could not resort to heroin like Cobain did. Eventually, however, this person found a solution and his pain went away before it was too late.
I am sorry that a stomach ache for cause of suicide is way less romantic than a general and existential torment, but I am not sorry at all. Suicide is not cool, it is not beautiful, and it is not something to make you dream or make Cobain look like the icon he became in spite of himself. And yes, reasons to die are often a lot more "trivial" than you may like. But if you had those insane stomach pains constantly and ceaselessly, you'd quickly understand how your life would be seriously ruined.
I did read somewhere that "Cobain sanctified his music through his suicide", as if Kurt had killed himself to give his art some special aura. In effect, it might have, though Led Zeppelin still live, and are no less of a legend because of it. Nevertheless, the idea that Cobain killed himself for that reason is preposterous: that is no reason to die. Nobody kills themselves for a reason like that. Least of all Cobain. He didn't seem very concerned about being famous, in the sense that he could very easily live without fame, and so I doubt that robbing himself of so many years of life to "immortalise" his music for who knows how long would have been a reason. The case remains open.
Rest in peace, Mister Cobain!