Language preservation is huge for native culture and identity, and it helps prevent assimilation (one of the reasons why the language and others like it were forcibly stamped out by the boarding schools which abducted Indian children from their parents.) There are even projects to teach Lushootseed to inmates in tribal jails, as a way of reconnecting prisoners with their culture and heritage. Iirc studies also show that depression and suicide are reduced if the native language stays alive.
There's a lot of debate and the Sapir-Whorf hypothesis has fallen out of favor with contemporary linguists, but I also feel like different languages encode different thought patterns. Lushootseed is nothing like English, and there are words specifically for tribal customs, religion and viewpoints that can't translate.
Overall, I see languages as living creatures. Extinction of minority languages or cultures is, to me, like species disappearing. Even if the biome doesn't suffer (and it can in both cases - Indians knew how to take care of the land before whites showed up), something sacred is lost v