If people evolved from apes, why are there still apes?
Short answer: Because apes have found a different method of survival.
Long answer: Because a rift valley opened up in Africa, allowing some apes* to move out of the forest into the new valley. Away from the trees, they found it helpful to stand erect. This gave them more efficient movement, the ability to use their hands for new functions, and the ability to see above the tall grass. Why didn't all creatures do this? Because there was also a good living to be made in the forest, which did not require this.
Some of these creatures lost some of their sense of sight and smell in order to develop cognitive brainpower. They were living in a new environment, and needed to figure out how to survive. Why didn't all creatures do this? Back in the forest, the sense of smell and sight were far too important for frivolous things like cognition.
Some of these creatures started to grow their brains larger after birth. This kept the head small enough to pass through the birth canal, but gave them cognitive advantages as adults. Why didn't all creatures do this? Brain development after birth slowed maturity. Other creatures did not have the net species brainpower needed to survive well while spending long periods caring for helpless infants.
Some of these creatures started to use simple tools in new, creative ways. Why didn't all creatures do this? They were not smart enough.
Some of these creatures saw sparks when they struck stones together, and learned how to harness them to make fires for warmth and protection. Why didn't all creatures do this? They did not have the brainpower, tools, or available hands.
Some of these creatures lost their hair and developed strong sweat glands. This allowed them to chase prey for a long time in the hot sun until the prey collapsed in exhaustion. Why didn't all creatures do this? They did not have fire and animal skins to keep them warm at nights, so they needed their hair.
Some of these creatures began to use fires to cook, making their food safer and easier to digest. Why didn't all creatures do this? They didn't know how to make fires.
Some of these creatures spent many hours talking about things around the campfire while their food cooked. They developed complex brains to understand complex communications. Why didn't all creatures do this? Their brains were too small to understand language.
Some of these creatures used their brain power to get more protein, so they could grow bigger brains, so they could get more protein, so they could get bigger brains, etc. Why didn't all creatures do this? They had been left out of this arms race long ago.
Some of these creatures learned to gossip. Gossiping left everybody know who they could trust and who they could not trust. They learned to build complex relationships based on freely helping each other. Then they would talk about who responded with reciprocity and who did not. If they tried to cheat, somebody would tell on them. Why didn't all creatures gossip? Gossiping requires brainpower.
Some of these creatures developed complex math skills. For instance, they learned to calculate the tide schedule, so they would leave the safety of their caves only in that short period of time when the tide made it optimal to find shellfish on the beach. Why didn't all creatures do this? Math is not for dummys.
Some of these creatures dominated the available resources, leaving intermediates and other competitors to die out for lack of resources. Why didn't all the competitors do this? They would have if they could have.
These surviving creatures became modern humans.
Meanwhile, the great apes stayed in the forest, remaining quite adept at a totally different lifestyle.
And that is why there are humans, and there are still apes.
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* Yes, I know, we did not evolve from modern apes. But we evolved from creatures that, if they were alive today, would be classified as apes.
Edit added 9/7/2020: Each of the steps listed above have scientific evidence. The actual details, reasons, and path may have been somewhat different than what is listed here. We are still learning. This was not intended to be a final, exact listing of the pathway to humanity. It is a listing of my understanding of the best evidenced pathway we now know.