Language isn't merely vocabulary, grammar and pronounciation. It's also nuance in expression, proverbs, slang, idioms. All of this is lost when content is translated and dubbed. When a person in a US sitcom uses an idiom, the spanish dubbed content translates to a similar Spanish idiom. With subtitles not only do I get the pronounciation and vocabulary, I also see in the subtitles a best-effort mapping from the english idiom to the corresponding idiom in my native language.
I think this is solving itself automatically as movies and traditional TV gives way for youtube and netflix where dubbed content isn't as common.