Well, not really a must, there isn't really a rule against making a 2 players game (at least as far as i know), and even it it were, i'd be applied only for this jam specifically, and not for all jams. Even said that, making a one player game is usually preferred, since not many jammers have friends to play it with, and thus having a one player game is more accessible for them... I just wanted to clarify that
Ps. Good feedback tho :3