We have a subtitle function on digital TV and radio broadcasting systems.
I think you're missing the point. The Deaf Aotearoa President put it best:
And, for many deaf people who use NZSL as their first or preferred language, NZSL is the only way to access information.
I think we have plenty to be proud of for actually choosing to engage deaf people via the means that they often prefer. Merely making do via subtitles (as some overseas governments choose to do instead) isn't as nice. And, yes, I am quite aware that we are in the digital age -- but thanks for your massive dose of enlightenment.