I'm a native English speaker and grew up mostly overseas in non-English speaking countries. Subtitles helped me understand American slang and conversational English that I wasn't used to hearing at home. I've also always struggled with distinctly understanding dialogue in films. It never had anything to do with active vs passive viewing. Another reason I always had them on was because I grew up in apartments and was always mindful of my noise levels for my neighbors. Using subtitles let me actively consume the film without worrying about bothering people around me. Now as an adult subtitles are my default for all media when available and I prefer it.
