Why birds never crash into each other in midair?
Evolution favored birds flying in flocks. So crash avoidance is "wired" into their nervous systems. That said, there are raptors like hawks and especially peregrine falcons that kill their prey by using the energy/momentum of a high speed dive to kill their prey. Even humans have a sort of crash avoidance reflex. But our evolution is nowhere near matching the pace of our technology in some situations.