I remember the BB's saying Rank is made up of several things. And is an overall indicator of all of them instead of just purely how good their max BBstats is.
1) Is strength of your teams ratings and opponents ratings in a given game
2) Overall consistency with your team and your opponents (so you or your opponent tanking are bad)
3) Trends. It's supposed to do some numbers magic to determine if your team is "on the rise" and will inflate your rank a bit to indicate your team is "going places". When I was in D2, I was ranked 5th in USA for half a season after losing in the Finals, I asked one of the BB's or possibly GM-Jason about it. The rankings system determined I was the best bet to promote out of D2 from any of the other D2 teams, so I was officially "on the rise" and "going places".
At one point like 5 or 6 seasons ago, II.4 had 3 teams in the Top 10 in USA. They basically got there because of #2, nobody in the league was ever tanking a game.