Thank you all for many answers. I partially found a satisfying answer in the phrase "the fact is, to most of the people who live on this planet it [living] does matter, and what happens to themselves and to those individuals they care about it matters."
I also agree that only a person who has his basic needs met has enough time to think about this possible futility of existence, yet perhaps there are some who are bugged by it even when they have no roof above their heads (fortunately not my case though).