the league structure is like this
d1 16 teams
d2 64 teams
d3 256 teams
d4 1024 teams
d5 4096 teams
so if everyone started in d4 season 1 the best 256 teams get to go to d3 season 2, then the best 64 go to d2 season 3 and season 4 you have the top 16 teams in d1 who earnt their way there
if there were less than 256 teams in a region it would be bad but the first season everyone would promote