Yeah you're right, but the goal of the game jam is to creating a new game idea, you can using your assets and code you already made in order to create that new game idea. For example if you make an ennemy sprite in a platformer, you can use it again in your new strategy game or even an other platformer but with a different concept. If you game looks like an existing one and the gameplay is exactly the same I don't see the point of participating in a game jam. It's not like that's a bad idea to make a second episode of your previous game, but not in a game jam.