@Nebu:
For example in a live game, if stalemate lines are built up, but someone still refuses to draw, even though he has zero chance to gain any new territories, just wants the opponent get tired and go to sleep, so you can progress then mods will step in.
You can't force others (in live game) to stay awake just because you don't want to draw.
This was just an example, but it is an example.
It also happens in 1 day+ phase games, you will get an email from the mods, what is your plan to finish the game? And if you can't give a decent answer how you will progress, they will draw it.
Also forcing cancel is legal, but certainly not a kind way of finishing the game. Generally speaking you can't force anyone within the rules to cancel. Until no rules are broken the game will and should continue, and if no progress can be made it will be drawn one way or the other.
In the example above 2 vs 2 in Ancient you should draw, you can't force cancel. There are no rules for that, as Geofram stated, but if the game is stuck, mods will interfere.
It's like step repetition in chess. It's an automatic draw otherwise players would sit there forever.