It is an old question like the human race itself. Explain why people speak multiple languages, which is very common in myths from cultures around the world. The story of the Babel Tower in the Bible is a famous example, but there are many other stories.
The truth is, we don't have an easy answer to why people speak multiple languages. That may be no reason. Instead, linguistic diversity is a reaction to the many different factors that we are just beginning to understand. We may not have the answers, but here are 6 factors that help new languages form.