The は particle doesn't mark the grammatical subject, or tell you anything else about what relationship the marked noun has with the rest of the sentence, like who is doing what. は marks the topic of conversation, which is just the context that the rest of the sentence depends on; in literal translations it often becomes something like "As for", but you can also just think of it like a headline or a movie title that cues the listener towards what is being talked about.
Japanese is also a high-context language, meaning that anything that would be obvious to the listener from context is able to go unsaid. This very often results in the grammatical subject being dropped, because it's usually clear who the speaker is talking about without them needing to be stated explicitly.
e.g. 今日は勉強しました = "As for today, (I) studied." → "Today" is the supporting context that doesn't have an actual grammatical role in the sentence, and "I" is unsaid because the subject is already clear from context
