I've worked with a couple different FLL teams before, and there seems to be a wide variety of types of kids who do it.

In some cases- they are kids who love to tinker with the parts but never actually get around to accomplishing the game.

However, to me this sounds a little bit more of a case where they didn't know exactly how to start. I know when I started diong FRC I had no idea what was going on, and was intimidated. Having a team definitely helps. In this case it might be particularly helpful to point out to the kids that it doesn't matter if its perfect- and just suggest they get started and build something thats fun. Once you get past the activation energy of starting to build something, it gets a lot easier. Have them make any mechanism they think would be cool- regardless of it would be applicable to the game.

Once they find it fun and interesting they may even find ways to implement these mechanisms. Hopefully, having time to just get started with it casually and not worry about if it works or not will help inspire them and make them want to have more meetings to work.