I feel that for a game jam, you already go into every game knowing that they will be small because of how short a time frame it was made in. Due to this, I focus on the gameplay, if it's fun and has some amount of variety, you could be playing it for hours despite being relatively small and simple. If you try to go too big, its more likely that it's not fully polished and not as fun, therefore even if it might have 2h of content, you might only play for 30mins before getting bored and leaving.