It's a question which has moidered humanity always, and attempts to answer it have caused much human misery. I think I remember that it was Simone de Beauvoir (who might have been, but wasn't, ever named Mrs Sartre) who said that people were always far too little occupied in living life and far too much pre-occupied with what life was for.
(Or words to similar effect, possibly.) But if you accept what Richard Dawkins and his forerunners (which I assume he had) have to say on the subject, it's really not all that difficult to understand how people came about, and then the question "Why?" drops away. The really fundamental basic question of Why has to do with why anything exists at all. This is one either for religion or physics (often both, especially if there's money in it!) There could so easily have been nothing, except that I once read that Nothing is far too unstable!
I remember hearing that biologists never need God, because all their material is given; but the problem of physicists is that they have to start from nothing, so they start looking ...