Because evolutions are random genetic mutations, so don't affect an entire species at once. Also environmental pressures play a part in shaping evolution. So, for example, apes under one set of circumstances might have to survive in a more demanding environment than apes under another. Thus [over aeons] that particular group might self-select for individuals with more dexterity / better problem-solving abilities, etc.
If evolution meant only the apex predator survived, there would only be humans in the world. Things evolve to exploit their environment - the snow leopard lives in the high mountains, the cheetah lives on the hot plains. You wouldn't expect the most evolved cat breed to exclude or preclude the existence of other cat breeds.