Assallamualeykum! Nowadays, people (especially young adults) have a strong desire to die. They hate this world, and those people are not always muslims. What could be the reason for their wish to die when they don't even know what expects them after death? they have absolutely no ambition. I can't say that they are in a high spiritual level either. however, some of them seem to be pretty self-sufficient. how can a person be self-sufficient possessing a hatred inside himself at the same time?
Alaikumassalam wa rahmatullah,
What you are describing is depression, and can be caused by genetic or environmental factors. A depressed person may be unable to think positive thoughts and to take joy in life, so they can become indifferent whether they live or die. People who are blessed with never having suffered depression can mistakenly think that it is negative thoughts that lead to depression. The reality is that it is the depression that causes the negative thoughts, and if the depression is cured, the negative thoughts will go away automatically.
For more on depression and its causes please see my essay Islam and Depression: A Survival Guide.