There are a few gamemodes this might be useful in, however we try and enable a timer to start fairly soon. For example, in bridges, a full 40 member lobby is not required for the game to start.
Waiting a little bit extra time allows players to naturally flow through games instead of having random people left out starting other games. This would honestly just create multiple small games instead of a few good sized games.
Finally, this could be an easily abused perk, and would be difficult to enforce or monitor.
I can see how this might things a bit more "fun" having players not have to stay in a lobby for too long, but that's the purpose of lobby parkours, and such
makes the lobby a bit more fun