It is not my sole reason, but I would lay somewhere around half of the desire upon loneliness and general feelings of being undesirable, useful but not wanted, and overall feeling that, as a person, I simply matter less than most of my peers. I have not been on a date in decades. Most of my interactions with other people are about how I can further their needs and wants.
Yet another year has gone by wherein my friends have not contacted me on my birthday, despite me doing this for them without fail, again and again. Perhaps I am fooling myself, but I like to think that I do a good impression of a person who does not think about these things. Around people, I am performing the part of someone for whom another cares, even if all evidence is to the contrary. I go to my job, I do my work. When I have a social event, that's work, too, but most likely busywork, nothing important is accomplished.
Overall, I view my death as being the conclusion of a natural process, like some diseased bit of flesh or a scab falling off, just the self-amputation of a completely unnecessary waste of skin: apoptosis for humanity. And after I go, people will perform the part of someone who is bereaved, over someone who was only an extra.
Polite applause for all of the actors when the curtain is drawn.