They aren't planned, they're simply generated upon all existing leagues being filled first (or nearly so). So just be patient (and invite some friends to play!) and wait for the current openings to fill up.
That may be awhile.Since new leagues are having a rough go of holding teams together and older leagues.I notice a big change every season in some leagues needing teams.It seems like every league that is in need of at least 5 new owners or more a season.