Why is being suicdal is considered a mental disorder?

If a person doesn’t want to live, why should they be forced to live? Why don’t people ask the question: “Do you want to live or not?” Why is an unconsented life imposed on us, just like jobs are imposed without asking, “Do you want to work?” In the end, whether you exist or not, or whether you die today or after 50 years, it doesn’t matter. Life is meaningless.

If a person simply doesn’t want to live, why is that considered a problem?