I have always known since I was five that death is a basic thought that comes in everyone's mind. People hate their lives sometimes, they just want to die. It's simple, isn't it? No, because there is something more to our tendency of hating our lives not everyone sees...
Strong Exterior
Life is a bitch, and this may sound degrading (I swear I don't mean it that way, so just focus on the analogy) but honestly when you fuck a bitch, you know you have to use some kind of protection in order to not knock her up or something, right? You fuck with life, you use defense mechanisms. Defense mechanisms make a strong exterior that prevents you from bearing seeds that could only cause more pain in your already cruel life you strive to just live with pure pleasure (I hope now the analogy makes sense).
Now, our strong exterior is a dead layer. I hate to admit it as a person with a hard shell myself, but it could really be pretty lifeless in a certain level. Some people forget about balance that they never allow themselves to strip free from that tough cover at least once in a while. Also be warned that this tough exterior does not only come as a literally strong character, for it also comes with an extremely soft facade that is actually utilized at its maximum as a form of silent weapon. Now, people with this delicate nature are usually the ones who find it difficult to just lay bare that they miss out on the pleasures of life that keep a person alive.
Basically, being tough and tender should always come together. When they don't, those who are too tough feel like death is the only solution to their lack of tenderness while for those who are too soft, they wish death upon themselves living the life where they choose not to brave the wilderness out there. Therefore, our perceived emptiness in life is not emptiness at all but rather an imbalance in decisions we ourselves make.
Death's Role
Life is all about that imbalance, and death has always given us the idea that all ends lead to new beginnings. Take the Christian view of death for example--you die and you either go to heaven and live happily or go to hell and still live but with endless suffering. However, death still remains a mysterious concept despite the ideas engraved in this society by the widely known Christianity. That space for skepticism is what makes each of us suicidal.
We already experience both joy and suffering in this life that it's not heaven or hell we look forward to when we want to die but that unknown we wish were anything but the life we despise. Somehow, it is easier to live life believing there is something else out there than figuring out how to achieve that balance while living, because even balance is as uncertain as what is really out there after death; it is just worse because you have to find it with a beaten up spirit and people around you. The balance our life seeks is not as easy as equally measured things placed into a whole. It's more of an ironic equality between everything in this life nobody could just express accurately and exactly.Meanwhile, death could be just anything a person perceives it to be, thus it is easier to invest on it. To hell with the complicated pursuit of balance when you're already dead on the inside anyway, right? Still, what-could've-been's are a strong influence as well, so a lot of us still choose to live.