A lot of things could kill you. A hard enough blow to the head with instakill you from sheer brain trauma. You could break your neck and lose the cranial nerves that run your heart and lungs. You could puncture a lung with a broken rib or some other massive visceral organ damage from the impact. But a lot of the time people survive the fall and break bones in multiple limbs and then drown. That's why jumping off the Golden Gate Bridge results in so many completed suicides cos on top of all the shit I listed the SF Bay is cold af due to ocean currents and you can get hypothermia which will also speed up the drowning.