We aren't horses or cows, which do exactly as you say and nearly never sleep.
Our species has evolved for at least 50 million years to sleep on tree tops in nests for the full night within a colony, viz all higher primates and many lesser ones all the way down to Lemurs. The homo genus, where we have evidence, has shown exactly the same patterns of sleep as modern humans. And add to that the last 400,000 after the invention of fire where any modern camper wouldn't have felt out of place inside any group of proto-humans.
Our species has evolved for at least 50 million years to sleep on tree tops in nests for the full night within a colony, viz all higher primates and many lesser ones all the way down to Lemurs. The homo genus, where we have evidence, has shown exactly the same patterns of sleep as modern humans. And add to that the last 400,000 after the invention of fire where any modern camper wouldn't have felt out of place inside any group of proto-humans.