Grammar is not rigid, it is just well defined. You can write a sentence in a dozen different ways, it is just that the meaning can be derived by a formal process.

Imagine you had to pass down a Java program (through oral tradition) to sort numbers and you had a Java Language Specification that remains unchanged. Now compare that to say English language where and you write an essay on sorting numbers. If both things are passed down orally over few dozen generations which one is likely to keep its form ?