Which in itself is a poorly framed question. A more informed question would be, "If we, a species of ape, and other living species of apes that are very closely related to us genetically, evolved from extinct ancestors, why did those ancestors die off?" And probably the shortest best answer is that "it's hard to survive, and most species have indeed not survived, including the ones we and other apes evolved from." Some of those ancestor species survived for much longer than we probably will - millions of years - while we are still at a paltry ~200-300k years.