The majority of those lost languages are spoken only, so we lose the culture's verbal history. Imagine if nobody ever decided to write down the Iliad.
What is now China with a few local variants was once covered in numerous dialects like India today, though not as numerous. However, one unifying language has led to a less fractured nation compared to say India or even Europe.
I'm not sure requirements can be said to be strict when the locals will tell you to your face that the mountains are high and the emperor far away.
Just because something is doesn't mean it's right. Tooth decay is also a natural process, as is myopia, and cancer.