Preserving languages is about preserving data for linguistics (and other fields). We preserve a lot of things with no "real value". We preserve fossils, species (any species with fewer than 100 remaining specimens isn't contributing to any ecosystem), books (even ones that are outdated and no one is ever likely to read), websites... I could go on all day. We preserve this stuff because we can learn by studying it.
Languages don't just have different nuances, they have completely different ways of putting human thought into words. They have grammars so different that a word for word translation would be no more readable than an untranslated text. They have such a huge variety of sounds that encoding them into IPA stretches the limits of Unicode's variants of the Latin alphabet, relying on many diacritic marks on top of regular characters.
It's not about preserving something that gives some greater ability to communicate. It's about preserving a database of linguistic evolution and the bounds of how human thought can be encoded orally.
Movies and TV did this too, but being broadcast media, they could - with state support - throw a fig leaf for "regional" languages.
People choose what language to speak. If they -- rather, we -- have a choice of languages, why do we choose common ones instead of uncommon ones? We are actively choosing to speak common languages, not some abstract network of computers is killing something.
If linguists or anyone else says we're doing something wrong and losing something valuable, why do we keep doing it?
Is it possible they're missing something, that maybe we gain more in choosing to understand each other than we're losing in ... in what, being able to read books that we haven't translated yet? In having a different set of nuances? Do any languages have a greater ability to describe thoughts than others? I suspect different languages have different nuances, but I doubt any has greater total ability to communicate.