Language is culture, and if the sapir-whorf hypothesis holds, different languages are literally different methods of thinking.
there are also other potential benefits, e.g. "the" in english gives little information about what noun may follow. "die/das/der" in general cut the probability space to a third.
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.
there are also other potential benefits, e.g. "the" in english gives little information about what noun may follow. "die/das/der" in general cut the probability space to a third.