I am afraid this is how current Tournament and Random minis are working.
You can sign up tournament mode even solo and if there is 12/12 the game will start. Problem is this: why join tournament solo if
1/ no one is using it so there is no one to play with
2/ if someone is using it (like a full group) you still need 5 more people for your team.
Not enough people are using it because they are not encouraged to do so. Random minis are for most part "easy picking" with a good chance of victory and tokens.