The reason is that without time 20 for both teams it's better to be in team 1 because you will get more time playing as sheep.
Without this condition it becomes rational to attempt to 'cheat' the picking order by playing worse/better depending on where you usually are so that you end up getting picked on team 1. You have to play to the level of the pick order you're aiming for e.g., 1 or 4 if you're usually 2/3. I used to do that, I played so I would consistently get picked forth ^^