I'm not the jam creator, but I don't think it's a competition, so we don't need to worry about any game "crushing" any other game. As far as giving time after the deadline ends to submit, I think you'll find a lot of tabletop game jams use this rule. Again, since this isn't a competition, the idea isn't to "weed out" entries but to encourage folks to finish a game and share it with the community.