There's been scientific studies proving that people enjoy stories more when they're spoiled. Essentially if we know the final outcome of the story we can focus more on the "how" than the "what." We notice the foreshadowing, feel tension as we see people moving towards their ultimate fates, etc.
Honestly, none of this is surprising, because throughout human history
most stories we were told were spoiled. Part of this was there were less stories, and those which were told (for example, as part of legend or mythology) were retold over and over. But even where this wasn't the case, you often had narrators openly tell you the fates of characters at the beginning of the story (like Romeo & Juliet, for example). Indeed, the entire dramatic form of the tragedy is based upon knowing that something awful is going to happen to the main character, and then seeing it unfold. There is no tension in the outcome, the tension is just how we get there.
I think the idea that story interest is on the basis of not knowing what will happen to the characters is relatively recent - probably dating to the rise of magazine serials in the 19th century, along with mystery writing. But the deeper history in storytelling is the journey to an already understood destination.
