Because we want you to retry. And retrying wouldn’t make any sense if you knew all the correct answers in advance, now would it? During the game, the only thing you know is whether your answer was correct or wrong. At the end of the game, you get an option to learn what the correct answers are. When you reveal all the correct answers, you can’t replay that round anymore, but you get to learn new words. A fair trade-off, methinks.