Which is pretty much true anyway when you think about it logically.
Looking at II.2 vs NBBA the TV Contract is 113,698 vs 196,317. 80K more a week there. If you promoted to the NBBA, you've got a roster worth more than 196K anyway. I'm in one of the middling D.III leagues and our average salary is more than that. So that's money in the bank.
If you just promoted, you're going to be filling out your Arena to the brim (assuming you're not overbuilt for the new league already), meaning you can either build out or raise prices. That's more incoming money, even if you raise your prices a very conservative 10%. Even if you try to tank it, assuming you take advantage of the higher league while you're in it, you'll more than make up the loss in fans on demotion by the amount you pocketed in additional TV cash and attendance gates from raised prices.
Over a season:
Raise in TV Contract: +1.12M
Raise in prices by 10% at a conservative 200K Arena income: +280K
Are you telling me that by tanking and gaining 1.4M, you're doing *worse* than if you had not promoted? I have a hard time believing that the fans lost by demotion are anywhere near worth the equivalent of a half a season's worth of home games completely lost. I'll be honest, I have no numbers to back up an NBBA->D.II demotion, but I can't imagine that it's *that* harsh.