Minions and Lanes

So the other day, I was wondering what would happen if nobody was on the lanes and just let the minions push. So I thought the lanes would simply stay freeze in the middle. So I created a costumed game. All thing I did was jungling. And I was the only champion in the game. I was blue side. my top lane got pushed in and my bot lane pushed in to enemy side, but mid lane pretty much freeze in the middle. So my question is, why would top and bot lane not freeze? If the minions are the same. they deal the same damage, wouldn't the lane just simply freeze?