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.