Humans and chimpanzees are very similar—genetically, behaviorally, physiologically. Underneath their fur, chimpanzees look sort of like human grandpas (only really, really buff).
But there's one big difference between chimps and humans that is curious once you think about it: Why don't chimps have hair? They have fur, sure, but why don't they have long flowing locks?
And why does animal fur seem to always grow to about the same length, while human hair keeps growing and growing?
Here, in a video answering fan questions, BBC Earth Unplugged's Maddie Moate and Simon Baxter explain that when it all comes down to it, human hair and animal fur are really the same thing. Just like chimpanzees, human hair will only grow to a certain length. This is obvious for arm and leg and back and other body hair. But it's also, more surprisingly, true for head hair, too. Skip to the 2:39 mark:
Human head hair, like chimp fur, lions' manes and back hair, will only grow to a specific, individually determined length, says Today I Found Out. That length is determined, in part, by the length of your hair's anagen, or growth, phase.
For the hair on your head, the average length of the anagen phase is about 2-7 years. For your arms, legs, eyebrows, etc., this phase usually lasts just 30-45 days. However, in extreme cases which are quite rare, some people have anagen periods for their heads as small as most people’s anagen phases for their arms and legs. For these people, their hair never naturally grows more than a few inches long, presumably saving them a significant amount of money over their lifetime on barber visits. ;-) The opposite is also true, with people whose anagen phase can last decades for their scalp hair. Both of these extremes are very rare though.
So chimps can't wear a bouffant for the same reason that your arm hair doesn't grow to the ground—genetics.