If humans came from apes, why do apes still exist?

The question makes complete sense as a first instinct, but it rests on a picture of evolution that isn't quite how it works. Evolution isn't a ladder where one species climbs up and leaves the old one behind. It's a branching tree, and a branch doesn't disappear just because a new one grows from the same trunk.

The common ancestor, not the modern ape

Roughly 6 to 8 million years ago, a population of primates existed that was ancestral to both humans and the great apes alive today, chimpanzees, bonobos, gorillas and others. At some point, groups within that ancestral population became geographically or behaviorally separated. One lineage eventually led to Homo sapiens. Another led to what we now call chimpanzees and bonobos. Another to gorillas. Each lineage kept evolving in its own direction under its own pressures, its own environment, its own food sources, its own predators.

No modern chimpanzee is your ancestor. You and a chimpanzee are more like very distant cousins who share great-great-grandparents, except the shared ancestor lived millions of years back, not in a family tree you could draw on paper.

Why the ancestor didn't "have" to go extinct

There's nothing in evolution that says the older form must disappear when a new one branches off. A species goes extinct when it can no longer survive its environment, not simply because a relative adapted somewhere else. Chimpanzees have been extraordinarily successful in their own ecological niche, the forests of central and west Africa, for millions of years. They didn't need to become human to survive. They had their own path.

The confusion often comes from a famous image you've probably seen: a row of figures marching from hunched ape to upright human. That image, called the March of Progress, was published by Time-Life Books in 1965 and was almost immediately criticized by scientists as misleading. It implies evolution is a straight line with a destination. It isn't. It's a sprawling bush with thousands of branches, most of which went extinct, and a few of which are still alive today, including both you and the chimpanzees.

What the evidence actually shows

Genetic sequencing has confirmed what the fossil record suggested. Humans and chimpanzees share roughly 98 to 99% of their DNA, which is the signature of a very recent common ancestor in evolutionary terms. The fossils of intermediate species, such as Australopithecus, which walked upright but had a much smaller brain than modern humans, fill in the steps along our specific branch. None of those intermediate forms are alive today, but the branch that led to chimpanzees had its own intermediates, which are also mostly gone.

The short version: apes still exist because evolution creates new branches without erasing old ones, and chimpanzees were never on their way to becoming human in the first place.