This is the way this is supposed to work: Netflix designs a service. People who don't enjoy service give feedback to Netflix. Netflix then decides how (and how quickly) to improve their service. If people are happy with this, then everyone wins. If people aren't, then they go and build their own service. If they succeed, then shame on Netflix for missing an opportunity. If they fail, then why should government regulation be have to get involved when the market proved this to be a bad idea (keep in mind, this is a video streaming service, not something really related to the pursuit of life, liberty & happiness).
It is very possible that the thought to add closed captioning crossed Netflix's mind, but then maybe they found it to be too expensive & possible illegal to implement this feature that wouldn't be used by their target audience. Maybe this feature is on their roadmap. There is also little precedence here. Not every screen on every movie is required to show closed captions. So why should Netflix be hamstrung by the government in this way?