One is triggered if there are network connectivity issues, in which case the game isn't scored for anybody. This is to get around the MMR abusers that would queue bots to leave on the other team so they would get a quick win.

The second state is usually triggered if a player has left after first blood. Even then, there are compensatory mechanisms. You lose less MMR than you would normally, and if a player leaves, your team will receive unreliable gold at a faster rate.