Because evolution doesn't care about making us happy. :( Nor keeping us alive permanently. Whatever passes on the genes passes with no regards to morality or optimal efficiency or anything like that. That being said, as a fellow sufferer, I can't help but ask everyday why this all had to happen to me, why I had to exist in the first place, and why I couldn't have just stayed nonexistent and oblivious instead of being thrown here suddenly and out of nowhere on this rock and forced to feel every second drag by before I'll be forced once again, to throw all those efforts and any attachments or connections away.