When speakers of a dying language learn a dominant one they don't lose their way of thinking, rather they adapt the dominant language to their needs. In this way the dominant language evolves. It's why there are ~180k english words but only 1200 Sindarian words.

While I agree that cultural loss is tragic, consider that it is inevitable. Homo Sapiens have existed for ~200,000 years. We only have SOME traces of SOME cultures for say 10k of those years. So from that lens, the vast majority of human culture has already been lost.