The main point about most causality questions is to answer the question “what if X did not happen / did happen”.

Normally you can’t get that information since you are looking at past events where X happened and you can’t change that. In addition to that it also helps answering questions where you could simulate a different behavior (as in a controlled random trial), but it’s simply too expensive / unethical / … (Is smoking really causing cancer, or not —- would X have had cancer if they didn’t smoke). Answering these kind of questions in a mathematical way gives a lot of power since it removes / kind of solves the correlation doesn’t equal causation problem