Nobody knowing for sure.

But it is natural, this works like a pirâmide, supose you are in a New server, If in level 1 you have 10 leagues, to level 2 only half Will be promote Making 5 leagues, but in level 3 you need 3 leagues, 42 teams, but only 35 Will promote, someone Will have to fill the remaining LEAGUE.
Promote a team is better that create a bot team.