One reason is simply that languages change over time, especially with relation to its culture. Meaning as a groups culture changes so does their language. In general languages having a notable change takes a few hundred years so it is a slow process.

So even if you want to assume there was a “first” language (which I don’t think is correct), over the thousands of years of human migration, our cultures have changed very drastically from one another and so do our languages.

That’s perverse

I need one of these for my yard