Why do cultures want to preserve their language?

Each language is important since they enable people to communicate and express themselves. When one dies out, future generations won't be able to understand that culture as they lost one vital part: language. This is why so many cultures want to preserve their language, as it is a vulnerable aspect of cultural heritage. However, despite efforts, a language dies out every two weeks. 

If you want to go the restroom then that's how you say it in Spanish :
Puedo ir al bano?