In 1965, Deaf Culture was first recognized as a real culture. That was only forty years ago. William Stokoe, Carl Croneberg, and Dorothy Casterline were the ones who introduced Deaf Culture to the world. They wrote the Dictionary of American Sign Language and included information about the thriving culture of the Deaf.
Before the Dictionary of American Sign Language was published, people involved in the medical field and deaf education only saw deaf people in terms of their deafness or hearing loss. They never would have though that Deaf people had their own culture.
The history of sign language is littered with shocking events. At several points in history, some not long ago, deaf people were strongly oppressed. At one point, they were even denied their basic rights. How their language, sign language, was treated during these oppressive times is directly related to why the deaf place such a high value on sign language today.