Relevant quote: "It is difficult to get a man to understand something, when his salary depends on his not understanding it." - Upton Sinclair
Until they see disruption or increased profits, I don't expect they'll change. I expect them to actually be disrupted before seeing it coming.
It isn't a good argument, but I could see it being made.
Translated subtitles would be copyrighted by the translator under a derivative license from the studio owning the film.
Subtitles of the type you suggest don't currently exist as standalone products; the level of detail and information you are describing would require the subtitles to be part of the film itself (see e.g., Atomic Blonde or John Wick for good examples).
Since using your own subtitle file, Netflix just doesn't have to do anything besides displaying them. Finding the correct subtitle is the users job, not Netflix. After all this would be called "use your own subtitle here" and I think Netflix can handle Unicode. Not everything has to be spoonfed for the dumbest user alive. Also, I don't think there is a reliable way to detect delays in the subtitle, especially if it's in a different language then the audio track. If you have a reference subtitle track, this might work, comparing time of first appearance. Any subsequent offset might be due to 25/23,976 which could be detected, but again, this is not Netflix's problem.
Everyone could have access to all movies/songs/books ever written with every subtitle file, dvd-only extra and whatnot they want. Could in the sense that it already exists and the marginal cost of delivering it to people is 0.
All that dealmaking, liscencing and such that you are describing... They're not strictly necessary. At least, they are not required to deliver the "goods." They are required in order to get revenue. Revenue requires pricing which requires exclusion, scarcity.
Not giving everyone everything is wasteful.
Sound is part of the film license in the US and Europe. This includes music and songs within the film. Studios pay out big bucks to license songs for films.
For example: my current employer would pay a license of approximately $500 to license major label music that will be played at an event to a live audience, broadcast globally, and streamed to 10 million viewers. (The total music budget for a 3-day event is maybe $5000, and that covers hours of music.) A movie studio licensing that same song for a movie would pay a minimum of $25,000, just for that song, assuming that it's part of the back catalog. A song that made the top 100 of the Billboard lists when it was released could command more than $100,000.
That's why sometimes the songs in the shows on Netflix are different than the ones on the DVDs, for example.
For whatever reason this is not the case for series in Netflix, which most of the time contain also in English subtitles. Wouldn't have helped the original commenter's case of course.
Just curious about the technicalities of copyright law.
Sadly, this has nothing to do with streaming and everything to do with rightsholders (aka "Hollywood").
The rights on the subtitles are held by the company that makes them, are then sold to the company that distributes the movie, which are then resold to regional distributors, separately from the rights to show the movie. This means that if you want to show, say Transformers, you have to negotiate with one company to show the picture, another company to license the sound, and yet another company for each set of subtitles.
It just isn't worth the effort in most cases to negotiate the Transformers English titles in France, for example.
Movie industry licensing and asset packaging are stuck in a time when you had to move physical reels of tape and film around, and still haven't caught up to digital technology.